l3vpn Working Group T. Morin, Ed.
Internet-Draft France Telecom R&D
Expires: June 18, 2006 December 15, 2005
Requirements for Multicast in L3 Provider-Provisioned VPNs
draft-ietf-l3vpn-ppvpn-mcast-reqts-03
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document presents a set of functional requirements for network
solutions that allow the deployment of IP multicast within L3
Provider Provisioned virtual private networks (PPVPNs). It specifies
requirements both from the end user and service provider standpoints.
It is intended that potential solutions specifying the support of IP
multicast within such VPNs will use these requirements as guidelines.
Working group
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This document is a product of the IETF's Layer 3 Virtual Private
Network (l3vpn) working group. Comments should be addressed to WG's
mailing list at <mailto:l3vpn@ietf.org>. The charter for l3vpn may
be found at <http://www.ietf.org/html.charters/l3vpn-charter.html>
Contributors
Main contributors to this document are listed below, in alphabetical
order :
o
Christian Jacquenet
France Telecom
3, avenue Francois Chateau
CS 36901 35069 RENNES Cedex
France
Email: christian.jacquenet@francetelecom.com [3]
o
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 [4]
o
Jean-Louis Le Roux
France Telecom R & D
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
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Email: jeanlouis.leroux@francetelecom.com [5]
o
Nicolai Leymann
T-Systems International GmbH
Engineering Networks, Products & Services
Goslarer Ufer 35
10589 Berlin, Germany
Email: nicolai.leymann@t-systems.com [6]
o
Renaud Moignard
France Telecom R & D
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
Email: renaud.moignard@francetelecom.com [7]
o
Thomas Morin
France Telecom R & D
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
Email: thomas.morin@francetelecom.com [8]
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Conventions used in this document . . . . . . . . . . . . . . 7
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 8
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Motivations . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. General Requirements . . . . . . . . . . . . . . . . . . . 9
3.3. Scaling vs. Optimizing Resource Utilization . . . . . . . 9
4. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1.1. Live content broadcast . . . . . . . . . . . . . . . . 11
4.1.2. Symetric applications . . . . . . . . . . . . . . . . 12
4.1.3. Data distribution . . . . . . . . . . . . . . . . . . 13
4.1.4. Generic multicast VPN offer . . . . . . . . . . . . . 13
4.2. Scalability orders of magnitude . . . . . . . . . . . . . 14
4.2.1. Number of VPNs with multicast enabled . . . . . . . . 14
4.2.2. Number of multicast VPNs per PE . . . . . . . . . . . 14
4.2.3. Number of CEs per multicast VPN per PE . . . . . . . . 14
4.2.4. PEs per multicast VPN . . . . . . . . . . . . . . . . 14
4.2.5. PEs with multicast VRFs . . . . . . . . . . . . . . . 15
4.2.6. Number of streams sourced . . . . . . . . . . . . . . 15
5. Requirements for supporting IP multicast within L3 PPVPNs . . 16
5.1. End user/customer standpoint . . . . . . . . . . . . . . . 16
5.1.1. Service definition . . . . . . . . . . . . . . . . . . 16
5.1.2. CE-PE Multicast routing and management protocols . . . 16
5.1.3. Quality of Service (QoS) . . . . . . . . . . . . . . . 16
5.1.4. SLA parameters measurement . . . . . . . . . . . . . . 18
5.1.5. Security Requirements . . . . . . . . . . . . . . . . 18
5.1.6. Monitoring and Troubleshooting . . . . . . . . . . . . 19
5.1.7. Extranet . . . . . . . . . . . . . . . . . . . . . . . 19
5.1.8. Internet Multicast . . . . . . . . . . . . . . . . . . 20
5.1.9. Carrier's carrier . . . . . . . . . . . . . . . . . . 20
5.1.10. Multi-homing, load balancing and resiliency . . . . . 21
5.1.11. RP Engineering . . . . . . . . . . . . . . . . . . . . 21
5.1.12. Addressing . . . . . . . . . . . . . . . . . . . . . . 21
5.1.13. Minimum MTU . . . . . . . . . . . . . . . . . . . . . 22
5.2. Service provider standpoint . . . . . . . . . . . . . . . 22
5.2.1. Scalability . . . . . . . . . . . . . . . . . . . . . 22
5.2.2. Resource optimization . . . . . . . . . . . . . . . . 24
5.2.3. Tunneling Requirements . . . . . . . . . . . . . . . . 25
5.2.4. Control mechanisms . . . . . . . . . . . . . . . . . . 26
5.2.5. Support of Inter-AS, inter-provider deployments . . . 27
5.2.6. Quality of Service Differentiation . . . . . . . . . . 27
5.2.7. Infrastructure security . . . . . . . . . . . . . . . 27
5.2.8. Robustness . . . . . . . . . . . . . . . . . . . . . . 28
5.2.9. Management tools, OAM . . . . . . . . . . . . . . . . 28
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5.2.10. Architectural Considerations . . . . . . . . . . . . . 29
5.2.11. Compatibility and migration issues . . . . . . . . . . 29
5.2.12. Troubleshooting . . . . . . . . . . . . . . . . . . . 30
6. Security Considerations . . . . . . . . . . . . . . . . . . . 31
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.1. Normative references . . . . . . . . . . . . . . . . . . . 33
8.2. Informative references . . . . . . . . . . . . . . . . . . 34
Appendix A. Requirements summary . . . . . . . . . . . . . . . . 38
A.1. General Requirements (Section 3) . . . . . . . . . . . . . 38
A.2. Scalability orders of magnitude (Section 4.2) . . . . . . 38
A.3. Requirements from mutlicast VPN customer standpoint
(Section 5.1) . . . . . . . . . . . . . . . . . . . . . . 38
A.4. Requirements from provider standpoint . . . . . . . . . . 42
Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . . 47
B.1. Changes between -00 and -01 . . . . . . . . . . . . . . . 47
B.2. Changes between -01 and -02 . . . . . . . . . . . . . . . 47
B.3. Changes between -02 and -03 . . . . . . . . . . . . . . . 48
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 49
Intellectual Property and Copyright Statements . . . . . . . . . . 50
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1. Introduction
VPN services satisfying requirement defined in [RFC4031] are now
being offered by many service providers throughout the world. VPN
services are popular because customers need not be aware of VPN
technologies deployed in the provider network. They scale well for
the following reasons:
o because P-routers need not be aware of VPN service details
o because the addition of a new VPN member requires only limited
configuration effort
There is also a growing need for support of IP multicast-based
services. Efforts to provide efficient IP multicast routing
protocols and multicast group management have been done in
standardization bodies which has led, in particular, to the
definition of the PIM and IGMP protocols.
However, multicast traffic is not natively supported within existing
L3 PPVPN solutions. Deploying multicast over an L3VPN today, with
only currently standardized solutions, requires designing customized
solutions which will be inherently limited in terms of scalability,
operational efficiency and bandwidth usage.
This document complements the generic L3 VPN requirements [RFC4031]
document, by specifying additional requirements specific to the
deployment of IP multicast-based services within PPVPNs. It
clarifies the needs from both VPN client and provider standpoints and
formulates the problems that should be addressed by technical
solutions with as a key objective to stay solution agnostic. There
is no intent to either specify solution-specific details in this
document or application-specific requirements. Also this document
does NOT aim at expressing multicast-inferred requirements that are
not specific to L3 PPVPNs.
It is expected that solutions that specify procedures and protocol
extensions for multicast in L3 PPVPNs SHOULD satisfy these
requirements.
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2. Conventions used in this document
2.1. Terminology
Although the reader is assumed to be familiar with the terminology
defined in [RFC4031], [RFC2547] and RFC2547bis [I-D.ietf-l3vpn-
rfc2547bis], PIM-SM [RFC2362], PIM-SSM [I-D.ietf-ssm-arch] the
following glossary of terms may be worthwhile.
Moreover we also propose here generic terms for concept that
naturally appears when multicast in VPNs is discussed.
ASM: Any Source Multicast. One of the two multicast service models
that denotes the source/receiver heuristic.
Multicast-enabled VPN, or multicast VPN: a VPN which supports IP
multicast capabilities, i.e. for which some PE devices (if not
all) are multicast-enabled and whose core architecture support
multicast VPN routing and forwarding
PPVPN: Provider-Provisioned Virtual Private Network
PE/CE: Provider/Customer edge Equipment ([RFC4026])
VRF or VR: By this phrase, we refer to the entity defined in a PE
dedicated to a specific VPN instance. "VRF" refers to [RFC2547]
terminology, and "VR" to the VR [I-D.ietf-l3vpn-vpn-vr]
terminology.
MD Tunnel: Multicast Distribution Tunnel, the means by which the
customer's multicast traffic will be conveyed across the SP
network. This is meant in a generic way: such tunnels can be
either point-to-point or point-to-multipoint. Although this
definition may seems to assume that distribution tunnels are
unidirectional, but the wording encompasses bi-directional tunnels
as well.
G: Denotes a multicast group
Multicast channel: (S,G) in the SSM model
Participating device: Refers to any network device that not only
participates to the deployment and the maintenance of the VPN
infrastructure, but also to the establishment and the maintenance
of the MD Tunnel (see above).
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S: Denotes a multicast source
SP: Service provider
SSM: Source Specific Multicast. One of the two multicast service
models where each corresponding service relies upon the use of a
single source.
RP: Rendez-vous point (PIM-SM [RFC2362])
Please refer to [RFC4026] for details about terminology specifically
relevant to VPN aspects, and to [RFC2432] for multicast performance
or QoS related terms.
2.2. Conventions
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].
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3. Problem Statement
3.1. Motivations
More and more L3 VPN customers use IP multicast services within their
private infrastructures. Naturally, they want to extend these
multicast services to remote sites that are connected via a VPN.
For instance, the customer could be a national TV channel with
several geographical locations that wants to broadcast a TV program
from a central point to several regional locations within its VPN.
A solution to support multicast traffic would consist in using point-
to-point tunnels across the provider network and requiring the PE
routers (provider's routers) to replicate traffic. This is obviously
sub-optimal as it places the replication burden on the PE and hence
has very poor scaling characteristics. It may also waste bandwidth
and control plane resources in the provider's network.
Thus, to provide multicast services for L3 VPN networks in an
efficient manner (that is, with scalable impact on signaling and
protocol state as well as bandwidth usage), in a large scale
environment, new mechanisms are required to enhance existing L3 VPN
solutions for proper support of multicast-based services.
3.2. General Requirements
This document sets out requirements for L3 provider-provisioned VPN
solutions designed to carry customers' multicast traffic. The main
requirement is that a solution SHOULD first satisfy requirements
documented in [RFC4031]: as far as possible, a multicast service
should have the same flavor as the unicast equivalent, including the
same simplicity (technology unaware), the same quality of service (if
any), the same management (e.g. monitoring of performances), etc.
Moreover, it also has to be clear that a multicast VPN solution MUST
interoperate seamlessly with current unicast solutions. It would
also make sense that multicast VPN solutions define themselves as
extensions to existing L3 provider-provisioned VPN solutions (such as
for instance, RFC2547bis [I-D.ietf-l3vpn-rfc2547bis] or VR [I-D.ietf-
l3vpn-vpn-vr]) and retain consistency with those, although this is
not a core requirement.
3.3. Scaling vs. Optimizing Resource Utilization
When transporting multicast VPN traffic over a service provider
network, there intrinsically is tension between scalability and
resource optimization, since the latter likely requires maintaining
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multicast state in the core network.
Consequently, some trade-off has to be made and this document will
express some requirements related to this trade-off.
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4. Use cases
The goal of this section is to highlight how different applications
and network contexts may have a different impact on how a multicast
VPN solution is designed, deployed and tuned. For this purpose we
describe some typical use case scenarios and express expectations in
terms of deployment orders of magnitude.
Most content of these sections originates from a survey done among
institutions and providers that expect to deploy such solutions, in
summer 2005. The full survey text, and raw results (13 responses)
were published separately and we only present here the most relevant
facts and expectations that the survey exposed.
For scalability figures, we considered that it was relevant to
highlight the highest expectations, those that are expected to have
the greatest impact on solution design ; for balance, we do also
mention cases were such high expectations were expressed only in few
answers.
4.1. Scenarios
We don't provide here an exhaustive set of scenarios that a mutlicast
VPN solution is expected to support - no solution should restrict the
scope of multicast applications and deployments that can be one over
a multicast VPN.
Hence, we only give here a short list of scenarios that are expected
to impact most the design of a multicast VPN solution.
4.1.1. Live content broadcast
Under this label, we group all applications that distribute content
(audio, video, or other content) with the property that this content
is expected to be consulted at once ("live") by the receiver. A
typical application are broadcast TV, production studios
connectivity, distribution of market data feeds.
The characteristics of such applications are the following:
o one or few sources to many receivers
o sources are often in known locations, receivers are in less
predictable locations (this latter point may depend on
applications)
o in some cases, it is expected that the regularity of audience
patterns may help improve how the bandwidth/state trade-off is
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handled
o the number of streams can be as high a hundreds, or even thousands
of streams
o bandwidth depend on the application, but may vary between a few
tens/hundreds Kb/s (e.g audio or low quality video media) and tens
of Mb/s (high quality video), with some demanding professional
applications requiring as much as hundreds of Mb/s.
o QoS requirement include, in many cases, a low multicast group join
delay
o QoS of these applications is likely to be impacted by packet loss
(some applications may be robust to low packet loss), and to have
low robustness against jitter
o delay sensitivity will depend on applications: some applications
are not so delay sensitive (e.g. broadcast TV), whereas others may
require very low delay (professional studio applications)
o some of these applications may involve rapid changes in customer
multicast memberships, but this will depend on audience and
capillarity of provider equipments
4.1.2. Symetric applications
Some use cases exposed by the survey can be grouped under this label,
and include many-to-many applications such as conferencing, clusters
monitoring.
Their characteristics is the relatively high number of streams that
they can produce, which has a direct impact on scalability
expectations.
A sub-case of this scenario is the case of symmetric applications
with small groups, when the number of receivers is low compared to
the number of sites in the VPNs (e.g.: video conferencing and
e-learning applications).
This latter case is expected to be an important input to solution
design, since it may impact a lot how the bandwidth/state is managed,
because :
o small groups, and low predictability of the location of
participants ("sparse groups")
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o and possibly significantly high bandwidth (a few Mb/s per
participant)
indicate that optimizing bandwidth may require introducing dedicated
states in the core network (typically as much as the number of
groups).
Last, some of these application may involve realtime interactions,
and will be highly sensitive to packet loss, jitter and delay.
4.1.3. Data distribution
Some applications which are expected to be deployed on multicast VPN
are non-realtime applications aiming at distributing data from few
sources and many receivers.
Such applications may be considered to have lower expectations than
their counterparts proposed in this document, since they would not
necessarily involve more data streams and are more likely to adapt
bandwidth and to be robust to packet loss, jitter and delay.
One important property is that such applications may involve higher
bandwidths (hundreds of Mb/s).
4.1.4. Generic multicast VPN offer
This ISP scenario is a deployment scenario where IP-Multicast
connectivity is proposed for every VPN : if a customer requests a
VPN, then this VPN will support IP-Multicast by default. In this
case the number of multicast VPNs equals the number of VPNs. This
implies a quite important scalability requirement (e.g. hundreds of
PEs, hundreds of VPNs per PE, with a potential increase by one order
of magnitude in the longer term).
The per mVPN traffic behaviour is not predictable because it's
completely up to the customer how the service is used. This results
in a traffic mix of the scenarios mentioned in section 4.1. QoS
requirements are similar to typical unicast scenarios, with the need
for different classes. Also in a such context, a reasonably large
range of protocols should be made available to the customer for use
at the PE-CE level.
Also, in such a scenario, customers may want to deploy multicast
connectivity between two or more multicast VPNs as well as access to
Internet Multicast.
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4.2. Scalability orders of magnitude
This section proposes orders of magnitude for different scalability
metrics relevant for multicast VPN issues. It should be noted that
the scalability figures proposed here relate to scalability
expectations of future deployments of multicast VPN solutions, as the
authors chose to not restrict the scope to the mere deployments known
as of today.
4.2.1. Number of VPNs with multicast enabled
From the survey results, we see an broad range of expectations.
There are extreme answers : from 5 VPNs (1 answer) to 10k VPNs (1
answer), but more typical answers are split between the low range
-tens of VPNs- (7 answers) or in the higher range of hundreds or
thousands of VPNs (2 + 4 answers).
A solution SHOULD support a number of multicast VPNs ranging from one
to several thousands.
4.2.2. Number of multicast VPNs per PE
The majority of survey answers express a number of multicast VPNs per
PE of around tens (8 responses between 5 and 50); a significant
number of them (4) expect deployments with hundreds or thousands (1
response) of multicast VPNs per PE.
A solution SHOULD support a number of multicast VPNs per PE of
several hundreds, and may have to scale up to thousands VPNs per PE.
4.2.3. Number of CEs per multicast VPN per PE
Survey responses span from 1 to 2000 CEs per multicast VPN per PE.
Most typical responses are between tens (6 answers) and hundreds (4
responses).
A solution SHOULD thus support a number of CEs per multicast VPN per
PE going up to several hundreds (and may target the support of
thousands of CEs).
4.2.4. PEs per multicast VPN
People who answered the survey typically expect deployments with
number of PEs per multicast VPNs in the range of hundreds of PEs (6
responses) or tens of PEs (4 responses). Two responses were in the
range of thousands (one mentioned a 10k figure).
A multicast VPN solution SHOULD support several hundreds of PEs per
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multicast VPN, and MAY usefully scale up to thousands.
4.2.4.1. ... with sources
The number of PEs, per VPNs, that would be connected to sources,
seems to be significantly lower than the number of PEs per VPNs.
This is obviously related to the fact many respondents mentioned
deployments related to content broadcast applications (one to many).
Typical numbers are of tens of source-connected-PEs (6 responses), or
hundreds (4 responses). One respondent expected a higher number of
several thousands.
A solution SHOULD support hundreds of source-connected-PEs per VPN,
and some deployment scenarios involving many-to-many applications,
may require supporting a number of source-connected-PEs equal to the
number of PEs (hundreds or thousands).
4.2.4.2. ... with receivers
The survey showed that the number of PEs with receivers is expected
to be of the same order of magnitude than the number of PEs in a
multicast VPN. This is consistent with the intrinsic nature of most
multicast applications, which have few source only participants.
4.2.5. PEs with multicast VRFs
A solution SHOULD scale up to thousands of PEs having multicast
service enabled.
4.2.6. Number of streams sourced
Survey responses led us to retain the following orders of magnitude
for the number of streams that a solution SHOULD support:
per VPN: hundreds or thousands of streams
per PE: hundreds of streams
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5. Requirements for supporting IP multicast within L3 PPVPNs
Again, the aim of this document is not to specify solutions but to
give requirements for supporting IP multicast within L3 PPVPNs.
In order to list these requirements we have taken two different
standpoints of two different important entities: the end user (the
customer using the VPN) and the service provider.
In the rest of the document, we mean by "a solution" or "a multicast
VPN solution", a solution that allows to perform multicast in an L3
provider provisioned VPN, and which addresses the requirements listed
in this document.
5.1. End user/customer standpoint
5.1.1. Service definition
As for unicast, the multicast service MUST be provider provisioned
and SHALL NOT require customer's devices (CE) to support any extra
feature compared to those required for multicast in a non-VPN
context.
5.1.2. CE-PE Multicast routing and management protocols
Consequently to Section 3.1, the CEs and PEs SHOULD employ existing
multicast protocols.
Such protocols SHOULD include : PIM-SM [RFC2362] (including PIM-SSM
[I-D.ietf-ssm-arch]), bidirectional PIM [I-D.ietf-pim-bidir], PIM-DM
[RFC3973], and IGMP (v1 [RFC1112], v2 [RFC2236] and v3 [RFC3376]).
Among those protocols, the support of PIM-SM (including SSM model)
and IGMP is REQUIRED (and MLD support is REQUIRED for IPv6
implementations). Bidir-PIM Support at the PE-CE interface is
RECOMMENDED. And considering deployments, PIM-DM is considered as
OPTIONAL.
When IPv6 is supported by a VPN solution, relevant IPv6 corresponding
protocols MUST also be supported, e.g. Multicast Listener Discovery
Protocol (MLD) (v1 [RFC2710]], v2 [RFC3810]]).
5.1.3. Quality of Service (QoS)
First, general considerations about QoS in L3 VPNs as developed in
section 5.5 of [RFC4031] are also relevant to this section.
QoS is measured in terms of delay, jitter, packet loss, and
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availability. These metrics are already defined for the current
unicast PPVPN services, and are included in Service Level
Agreements(SLA). In some cases, provided SLA may be different
between unicast and multicast, which will need service
differentiation mechanisms as such.
The level of availability for the multicast service SHOULD be on par
with what exists for unicast traffic. For instance same traffic
protection mechanisms SHOULD be available for customer multicast
traffic when it is carried over the service provider's network.
A multicast in VPN solution shall allow to define at least the same
level of quality of service than what exists for unicast, and than
what exists for multicast in a non-VPN context. From this
perspective, the deployment of multicast-based services within an L3
PPVPN environment SHALL benefit from DiffServ [RFC2475] mechanisms
that include multicast traffic identification, classification and
marking capabilities, as well as multicast traffic policing,
scheduling and conditioning capabilities. Such capabilities MUST
therefore be supported by any participating device in the
establishment and the maintenance of the multicast distribution
tunnel within the VPN.
As multicast is often used to deliver high quality services such as
TV broadcast, the solution should have additional features to support
high QoS such as bandwidth reservation and admission control.
Also, considering that multicast reception is receiver-triggered,
group join delay (as defined in [RFC2432]) is also considered one
important QoS parameter. It is thus RECOMMENDED that a multicast VPN
solution be designed appropriately in this regard.
The group leave delay (as defined in [RFC2432]) may also be important
on the CE-PE link for some usage scenarios : in cases where the
typical bandwidth of multicast streams is close to the bandwidth a
PE-CE link, it will be important to have the ability to stop the
emission of a stream on the PE-CE link as soon as it stops being
requested by the CE, to allow for fast switching between two
different high throughput multicast streams. This implies that it
SHOULD be possible to tune the multicast routing or group management
protocols (e.g. IGMP/MLD or PIM) used on the PE-CE adjacency to
reduce the group leave delay to the minimum.
Last, 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. Packet loss issues have also to
be considered when a new source starts to send traffic to a group:
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any receiver interested in receiving such traffic SHOULD be serviced
accordingly.
5.1.4. SLA parameters measurement
As Service Level Agreement (SLA) parameters are part of the service
that is sold, they are often monitored. The monitoring is used for
technical reasons by the service provider and is often sold to the
customer for end-to-end service purposes.
The solution MUST support SLA monitoring capabilities, which MAY
possibly rely upon similar techniques (than those used by the unicast
for the same monitoring purposes).
Multicast specific characteristics that may be monitored are, for
instance, multicast statistics per stream, end-to-end delay and group
join delay (time to start receiving a multicast group traffic across
the VPN, as defined in [RFC2432] section 3).
A generic discussion of SLAs is provided in [RFC3809].
5.1.5. Security Requirements
Security is a key point for a customer who uses subscribes to a VPN
service. The RFC2547bis [I-D.ietf-l3vpn-rfc2547bis] model offers
some guarantees concerning the security level of data transmission
within the VPN.
A multicast VPN solution MUST provide an architecture with the same
level of security for both unicast and multicast traffic.
Moreover, the activation of multicast features SHOULD be possible:
o with a VRF or VR granularity
o with a CE granularity (when multiple CE of a same VPN are
connected to a common VRF)
o with a distinction between multicast reception and emission
o with a multicast group and/or channel granularity
A multicast VPN solution may choose to make the optimality/
scalability trade-off stated in Section 3.3 by sometimes distributing
multicast traffic of a client group to a larger set of PE routers
that may include PEs which are not part of the VPN. From a security
standpoint, this may be a problem for some VPN customers, thus a
multicast VPN solution using such a scheme MAY offer ways to avoid
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this for specific customers (and/or specific customer multicast
streams).
5.1.6. Monitoring and Troubleshooting
A service provider and its customers MUST be able to manage the
capabilities and characteristics of their multicast VPN services.
Automated operations and interoperability with standard management
platforms SHOULD be supported.
Service management should also include the TMN 'FCAPS'
functionalities, as follows: Fault, Configuration, Accounting,
Provisioning, and Security.
The monitoring of multicast specific parameters and statistics SHOULD
include :
o multicast traffic statistics: total traffic conveyed, incoming,
outgoing, dropped, etc., by period of time (as a MUST)
o IP Performance Metrics related information (IPPM, [RFC2330]) that
is relevant to the multicast traffic usage: such information
includes the one-way packet delay, the inter-packet delay
variation, etc. (as a MAY)
Apart from statistics on multicast traffic, customers of a multicast
VPN will need information concerning the status of their multicast
resource usage (state and bandwidth). Indeed, as mentioned in
Section 5.2.4, for scalability purposes, a service provider may limit
the number (and/or throughput) of multicast streams that are received
and produced at a client site, and so a multicast VPN solution SHOULD
allow customers to find out their current resource usage (state and
throughput), and to receive some kind of feedback if their usage
exceed bounds. Whether this issue will be better handled at the
protocol level at the PE-CE interface or via the ISP customer
support, needs further discussion.
5.1.7. Extranet
In current PP L3VPN models, a customer site may be setup to be part
of multiple VPNs and this should still be possible when a VPN is
multicast-enabled. In practice it means a VRF or VR will be part of
more than one VPN.
A multicast VPN solution MUST support such deployments.
More precisely this means that a multicast VPN solution MUST offer
means so that:
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o receivers behind attached CEs can receive multicast traffic
sourced in any of the VPNs (if security policy permits)
o sources behind attached CEs can reach multicast traffic receivers
located in any of the VPNs
o multicast can be independently enabled for the different VPNs (and
multicast reception and emission can also be independently
enabled)
Proper support for this feature SHOULD not require replicating
multicast traffic on a PE-CE link, whether it is a physical or
logical link.
For instance, it must be possible to configure a VRF so that an
enterprise site participating to a BGP/MPLS multicast-enabled VPN and
connected to that VRF, can receive a multicast stream from, [or
originate a multicast stream towards], another VPN that would be
associated to that VRF.
5.1.8. Internet Multicast
Connectivity with Internet Multicast (as a source or receiver)
somehow fits in the context of the previous section.
It should be considered OPTIONAL given additional considerations
needed to fulfill requirements for Internet side, such as security
treatment.
5.1.9. Carrier's carrier
Many L3 PPVPN solutions, such as RFC2547bis [I-D.ietf-l3vpn-
rfc2547bis] and VR [I-D.ietf-l3vpn-vpn-vr] define the "Carrier's
Carrier" model, where a "carrier's carrier" service provider supports
one or more customer ISP, or "sub-carriers". A multicast VPN
solution SHOULD support the carrier's carrier model in a scalable and
efficient manner.
Ideally the range of tunneling protocols available for the sub-
carrier ISP should be the same as those available for the carrier's
carrier ISP. This implies that the protocols that may be used at the
PE-CE level SHOULD NOT be restricted to protocols required as per
Section 5.1.2 and SHOULD include some of the protocols listed in
Section 5.2.3.
In the context of MPLS-based L3VPN deployments, such as BGP/MPLS VPNs
[I-D.ietf-l3vpn-rfc2547bis], this means that MPLS label distribution
SHOULD happen at the PE-CE level, giving the ability to the sub-
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carrier to use multipoint LSPs as a tunneling mechanism.
5.1.10. Multi-homing, load balancing and resiliency
A multicast VPN solution should be compatible with current solutions
that aim at improving the service robustness for customers such as
multi-homing, CE-PE link load balancing and failover. A multicast
VPN solution SHOULD also be able to offer those same features for
multicast traffic.
Any solution SHOULD support redundant topology of CE-PE links. It
SHOULD minimize multicast traffic disruption and failover.
On the other hand, it is also necessary to care about failover
mechanisms that are unique to multicast routing control. For
instance, if the customer uses some control mechanism for RP
redundancy on PIM-SM (e.g. BSR), it SHOULD work transparently
through that VPN.
5.1.11. RP Engineering
When PIM-SM (or bidir-PIM) is used in ASM mode on the VPN customer
side, the location of the RP has to be chosen. In some cases this
engineering problem is not trivial: for instance, if sources and
receivers are located in VPN sites that are different than that of
the RP, then traffic may flow twice through the SP network and the
CE-PE link of the RP (from source to RP, and then from RP to
receivers) ; this is obviously not ideal. A multicast VPN solution
SHOULD propose a way to help on solving this RP engineering issue.
Moreover, some service providers offer to manage customer's multicast
protocol operation on behalf of them. This implies that it is needed
to consider cases where the customer's RPs are outsourced (e.g., on
PEs).
5.1.12. Addressing
A multicast provider-provisioned L3VPN SHOULD NOT impose restrictions
on multicast group addresses used by VPN customers.
In particular, like unicast traffic, an overlap of multicast group
address sets used by different VPN customers MUST be supported.
The use of globally unique means of multicast-based service
identification at the scale of the domain where such services are
provided SHOULD be recommended. If the ASM model is used, this
implies the use of the multicast administratively scoped range,
(239/8 as per [RFC2365]) for services which are to be used only
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inside the VPN, and of globally assigned group addresses for services
for which traffic may be transmitted outside the VPN (e.g. GLOP
[RFC3180]).
5.1.13. Minimum MTU
For customers, it is often a serious issue whether transmitted
packets will be fragmented or not. In particular, some multicast
applications might have different requirements than those that make
use of unicast, and they may expect services that guarantee available
packet length not to be fragmented.
Therefore, a multicast VPN solution SHOULD let customers' devices be
free of any fragmentation or reassembly activity.
A committed minimum path MTU size SHOULD be provided to customers.
Moreover, since Ethernet LAN segments are often located at first and
last hops, a minimum 1500 bytes IP MTU SHOULD be provided.
It SHOULD also be compatible with Path MTU discovery mechanisms, such
as those defined in [RFC1191] or [I-D.mathis-frag-harmful].
5.2. Service provider standpoint
Note: please remember that, to avoid repetition and confusion with
terms used in solution specifications, we introduced in Section 2.1
the term MDTunnel (for Multicast Distribution Tunnel), which
designates the data plane means used by the service provider to
forward customer multicast traffic over the core network.
5.2.1. Scalability
Some currently standardized and deployed L3VPN solutions have the
major advantage of being scalable in the core regarding the number of
customers and the number of customer routes. For instance, in the
RFC2547bis [I-D.ietf-l3vpn-rfc2547bis] and VR [I-D.ietf-l3vpn-vpn-vr]
models, a P-router sees a number of MPLS tunnels that is only linked
to the number of PEs and not to the number of VPNs, or customers'
sites.
As far as possible, this independence in the core, with respect to
the number of customers and to customer activity, is recommended.
Yet, it is recognized that in our context scalability and resource
usage optimality are competing goals, so this requirement may be
reduced to giving the possibility of bounding the quantity of states
that the service provider needs to maintain in the core for
MDTunnels, with a bound being independent of the multicast activity
of VPN customers.
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It is expected that multicast VPN solutions will use some kind of
point point-to-multipoint technology to efficiently carry multicast
VPN traffic, and that such technologies require maintaining state
information, and will use resources in the control plane (memory and
processing, and possibly address space).
Scalability is a key requirement for multicast VPN solutions.
Solutions MUST be designed to scale well with an increase in the
number of any of the following:
o the number of PEs
o the number of customers VPNs (total and per PE)
o the number of PEs and sites in any VPN
o the number of client multicast channels (groups or source-groups)
Please consult, section 4.2 for typical orders of magnitude up to
which a multicast VPN solution is expected to scale
Scalability of both performance and operation MUST be considered.
Key considerations SHOULD include:
o the processing resources required by the control plane
(neighborhood or session maintenance messages, keep-alives,
timers, etc.)
o the memory resources needed for the control plane
o the amount of protocol information transmitted to manage a
multicast VPN (e.g. signalling throughput)
o the amount of control plane processing required on PE and P to add
remove a customer site (or a customer from a multicast session)
o the number of multicast IP addresses used (if IP multicast in ASM
mode is proposed as a multicast distribution tunnel)
o other particular elements inherent to each solution that impacts
scalability (e.g., if a solution uses some distribution tree
inside the core, topology of the tree and number of leaf nodes may
be some of them)
It is expected that the applicability of each solution will be
evaluated with regards to the aforementioned scalability criteria.
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These considerations naturally lead us to believe that proposed
solutions SHOULD offer the possibility of sharing such resources
between different multicast streams (between different VPNs, between
different multicast streams of the same or of different VPNs). This
means for instance, if MDTunnels are trees, being able to share an
MDTunnel between several customers.
Those scalability issues are expected to be more significant on
P-routers, but a multicast in VPNs solution should address both P and
PE routers as far as scalability is concerned.
5.2.2. Resource optimization
5.2.2.1. General goals
One of the aims of the use of multicast instead of unicast is
resource optimization in the network.
The two obvious suboptimal behaviors that a multicast VPN solution
would want to avoid are needless duplication (when same data travels
twice or more on a same link, e.g. when doing ingress PE replication)
and needless reception (e.g. a PE receiving traffic that it does not
need because there are no downstream receivers).
5.2.2.2. Trade-off and tuning
As previously stated in this document, designing a scalable solution
that makes an optimal use of resources is considered difficult. Thus
what is expected from a multicast VPN solution is that it addresses
the resource optimization issue while taking into account the fact
that some trade-off has to be made.
Moreover, it seems that a "one size fits all" trade-off probably does
not exist either. Thus a multicast VPN solution SHOULD offer the
service providers appropriate configuration settings that let them
tune the trade-off according to their peculiar constraints (network
topology, platforms, customer applications, level of service offered
etc.).
As an illustration here are some example bounds of the trade-off
space:
Bandwidth optimization: setting up somehow optimal core MDTunnels
whose topology (PIM or P2MP LSP trees, etc.) precisely follows
customer's multicast routing changes. This requires managing an
important quantity of states in the core, and also quick reactions
of the core to customer multicast routing changes. This approach
can be advantageous in terms of bandwidth, but it is bad in terms
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of state management.
State optimization: setting up MDTunnels that aggregate multiple
customer multicast streams (all or some of them, across different
VPNs or not). This will have better scalability properties, but
at the expense of bandwidth since some MDTunnel leaves will very
likely receive traffic they don't need, and because increased
constraints will make it harder to find optimal MDTunnels.
5.2.2.3. Traffic engineering
If the VPN service provides traffic engineering features for the
connection used between PEs for unicast traffic in the VPN service,
the solution SHOULD provide equivalent features for multicast
traffic.
A solution SHOULD offer means to support key TE objectives as defined
in [RFC3272], for the multicast service.
A solution MAY also usefully support means to address multicast-
specific traffic engineering issues: it is known that bandwidth
resource optimization in the point-to-multipoint case is a NP-hard
problem, and that techniques used for unicast TE may not be
applicable to multicast traffic.
Also, it has been identified that managing the trade-off between
resource usage and scalability may incur uselessly sending traffic to
some PEs participating in a multicast VPN. For this reason, a
multicast VPN solution MAY permit that the bandwidth/state tuning
take into account the relative cost or availability of bandwidth
toward each PE.
5.2.3. Tunneling Requirements
5.2.3.1. Tunneling technologies
Following the principle of separation between the control plane and
the forwarding plane, a multicast VPN solution SHOULD be designed so
that control and forwarding planes are not inter-dependent: the
control plane SHALL NOT depend on which forwarding plane is used (and
vice versa), and the choice of forwarding plane SHOULD NOT be limited
by the design of the solution. The solution SHOULD also NOT be tied
to a specific tunneling technology.
In a multicast VPN solution extending a unicast L3 PPVPN solution,
consistency in the tunneling technology has to be privileged: such a
solution SHOULD allow the use of the same tunneling technology for
multicast as for unicast. Deployment consistency, ease of operation
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and potential migrations are the main motivations behind this
requirement.
For MDTunnels (multicast distribution tunnels, the means used to
carry VPNs' multicast traffic over the provider's network), a
solution SHOULD be able to use a range of tunneling technologies,
including point-to-point and point-to-multipoint, such as GRE
[RFC2784] (including GRE in multicast IP trees), MPLS [RFC3031]
(including P2P or MP2P tunnels, and multipoint tunnels signaled with
MPLS P2MP extensions to RSVP [I-D.ietf-mpls-rsvp-te-p2mp] or LDP
[I-D.leroux-mpls-mp-ldp-reqs][I-D.minei-wijnands-mpls-ldp-p2mp]),
L2TP (including L2TP for multicast [RFC4045]), IPsec [RFC2401], IP-
in-IP [RFC1853], etc.
Naturally, it is RECOMMENDED that a solution is built so that it can
use the point to multipoint variants of these techniques, that allow
for packet replications to happen along a tree in the provider core
network, and may help improve bandwidth efficiency in our multicast
VPN context.
5.2.3.2. MTU and Fragmentation
A solution SHOULD support a method that provides the minimum MTU of
the MDTunnel (e.g., to discover MTU, to tell MTU with signaling,
etc.) so that :
o fragmentation inside the MDTunnel -even when allowed by the
tunneling technology used- does not happen
o proper troubleshooting can be done if packets too big for the
MDTunnel happen to be encapsulated in the MDTunnel
5.2.4. Control mechanisms
The solution MUST provide some mechanisms to control the sources
within a VPN. This control includes the number of sources that are
entitled to send traffic on the VPN, and/or the total bit rate of all
the sources.
At the reception level, the solution MUST also provide mechanisms to
control the number of multicast groups or channels VPN users are
entitled to subscribe to and/or the total bit rate represented by the
corresponding multicast traffic.
All these mechanisms MUST be configurable by the service provider in
order to control the amount of multicast traffic and state within a
VPN.
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Moreover it MAY be desirable to be able to impose some bound on the
quantity of state used by a VPN in the core network for its multicast
traffic, whether on each P or PE router, or globally. The motivation
is that it may be needed to avoid out-of-resources situations (e.g.
out of memory to maintain PIM state if IP multicast is used in the
core for multicast VPN traffic, or out of memory to maintain RSVP
state if MPLS P2MP is used, etc.).
5.2.5. Support of Inter-AS, inter-provider deployments
A solution MUST support inter-AS multicast VPNs, and SHOULD support
inter-provider mutlicast VPNs. Considerations about coexistence with
unicast inter-AS VPN Options A, B and C (as described in section 10
of RFC2547bis [I-D.ietf-l3vpn-rfc2547bis]) are strongly encouraged.
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.
o 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)
o If a solution does require a single tunnel to span P routers in
multiple ASs, the solution SHOULD provide mechanisms to ensure
that the inter-provider co-ordination to setup such a tunnel is
minimized
Moreover such support SHOULD be possible without compromising other
requirements expressed in this requirement document, and SHALL NOT
incur penalty on scalability and bandwidth usage.
5.2.6. Quality of Service Differentiation
A multicast VPN solution SHOULD give a VPN service provider the
ability to offer, guarantee and enforce differentiated levels of QoS
for its different customers.
5.2.7. Infrastructure security
The solution shall provide the same level of security for the service
provider as what currently exist for unicast VPNs. For instance,
that means that the intrinsic protection against DOS and DDOS attacks
of the BGP/MPLS VPN solution must be equally supported by the
multicast solution.
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Moreover, since multicast traffic and routing are intrinsically
dynamic (receiver-initiated), some mechanism SHOULD be proposed so
that the frequency of changes in the way client traffic is carried
over the core can be bounded and not tightly coupled to dynamic
changes of multicast traffic in the customer network. For example,
multicast route dampening functions would be one possible mechanism.
Network devices that participate in the deployment and the
maintenance of a given L3 VPN MAY represent a superset of the
participating devices that are also involved in the establishment and
the maintenance of the multicast distribution tunnels. As such the
activation of IP multicast capabilities within a VPN SHOULD be
device-specific, not only to make sure that only the relevant devices
will be multicast-enabled, but also to make sure that multicast
(routing) information will be disseminated to the multicast-enabled
devices only, hence limiting the risk of multicast-inferred DOS
attacks.
Unwanted multicast traffic (e.g. multicast traffic that may be sent
by a source located somewhere in the Internet and for which there is
no interested receiver connected to a given VPN infrastructure) MUST
NOT be propagated within a multicast-enabled VPN.
Security considerations are particularly important for inter-AS and
inter-provider deployments. In a such perspective, it is RECOMMENDED
that a multicast VPN solution support means to ensure the integrity
and authenticity of multicast-related exchanges across inter-ASes or
inter-provider borders.
Last, control mechanisms described in previous section are also to be
considered from this infrastructure security point of view.
5.2.8. Robustness
Resiliency is also crucial to infrastructure security, thus a
multicast VPN solution SHOULD whether avoid single points of failures
or propose some technical solution making possible to implement a
fail-over mechanism.
As an illustration, one can consider the case of a solution that
would use PIM-SM as a means to setup MDTunnels. In such a case, the
PIM RP might be a single point of failure. Such a solution should
thus be compatible with a solution implementing RP resiliency.
5.2.9. Management tools, OAM
The operation of a multicast VPN solution SHALL be as light as
possible and providing automatic configuration and discovery SHOULD
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be prioritized. Particularly the operational cost of setting up
multicast on a PE should be as low as possible.
Moreover, monitoring of multicast specific parameters and statistics
SHOULD be offered to the service provider.
Most notably the provider SHOULD have access to:
o Multicast traffic statistics (total traffic conveyed, incoming,
outgoing, dropped, etc., by period of time) - Information about
client multicast resource usage (state and throughput)
o The IPPM (IP Performance Metrics [RFC2330]) -related information
that is relevant to the multicast traffic usage: such information
includes the one-way packet delay, the inter-packet delay
variation, etc.
o Alarms when limits are reached on such resources - Statistics on
decisions related to how client traffic is carried on distribution
tunnels (e.g. "traffic switched onto a multicast tree dedicated to
such groups or channels")
o Statistics on parameters that could help the provider to evaluate
its optimality/state trade-off
All or part of this information SHOULD be made available through
standardized SNMP ([RFC1157]) MIBs (Management Information Base).
5.2.10. Architectural Considerations
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 unicast VPN, the
balance between their advantage and operation burden should be
examined thoroughly.
5.2.11. Compatibility and migration issues
It is a requirement that unicast and multicast services MUST be able
to co-exist within the same VPN.
Likewise, the introduction of IP multicast VPN capabilities in
devices that participate to the deployment and the maintenance of a
multicast VPN SHOULD be as smooth as possible, i.e. without affecting
the overall quality provided with the services that are already
supported by the underlying infrastructure.
A multicast VPN solution SHOULD prevent compatibility and migration
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issues, for instance by prioritizing mechanisms facilitating forward
compatibility. Most notably a solution supporting only a subset of
those requirements SHOULD be designed to be compatible with future
enhanced revisions.
It SHOULD be an aim of any multicast VPN solution to offer as much
backward compatibility as possible. Ideally a solution would have be
the ability to offer multicast VPN services across a network
containing some legacy routers not supporting any multicast VPN
specific features.
In any case a solution SHOULD state a migration policy from possibly
existing deployments.
5.2.12. Troubleshooting
A multicast VPN solution that dynamically adapts the way some client
multicast traffic is carried over the provider's network may incur
the disadvantage of being hard to troubleshoot. In such a case, to
help diagnose multicast network issues, a multicast VPN solution
SHOULD provide monitoring information describing how client traffic
is carried over the network (e.g. if a solution uses multicast-based
MDTunnels, which provider multicast group is used for such and such
client multicast stream). A solution MAY also provide configuration
options to avoid any dynamic changes, for multicast traffic of a
particular VPN or a particular multicast stream.
Moreover, a solution MAY usefully provide some mechanism letting
network operators check that all VPN sites that advertised interest
in a particular customer multicast stream are properly associated
with the corresponding MDTunnel. Providing the operators with means
to check the proper setup and operation of MDTunnels MAY also be
provided (e.g. when MPLS is used for MDTunnels, integrating
mechanisms such as LSPPing[I-D.ietf-mpls-lsp-ping][I-D.ietf-mpls-
p2mp-lsp-ping] into the L3VPN troubleshooting functionalities will be
desirable). Depending on the implementation such verification could
be initiated by source-PE or receiver-PE.
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6. Security Considerations
This document does not by itself raise any particular security issue.
A set of security issues have been identified that MUST be addressed
when considering the design and deployment of multicast-enabled VPN
networks. Such issues have been described in Section 5.1.5 and
Section 5.2.7.
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7. Acknowledgments
The authors would like to thank, by rough chronological order,
Vincent Parfait (Equant), Zubair Ahmad (Equant), Elodie Hemon-
Larreur, Sebastien Loye (France Telecom), Rahul Aggarwal (Juniper),
Hitoshi Fukuda (NTT Communications), Luyuan Fang (AT&T), Adrian
Farrel, Daniel King, Yiqun Cai (Cisco), Ronald Bonica, Len Nieman,
Satoru Matsushima (Japan Telecom), Netzahualcoyotl Ornelas (Renater),
for their review, valuable input and feedback.
We also thank the people who kindly answered the survey, and Daniel
King who took care of gathering and anonymizing its results.
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8. References
8.1. Normative references
[RFC3978] Bradner, S., "IETF Rights in Contributions", BCP 78,
RFC 3978, March 2005.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4031] Carugi, M. and D. McDysan, "Service Requirements for Layer
3 Provider Provisioned Virtual Private Networks (PPVPNs)",
RFC 4031, April 2005.
[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual
Private Network (VPN) Terminology", RFC 4026, March 2005.
[RFC2362] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering,
S., Handley, M., and V. Jacobson, "Protocol Independent
Multicast-Sparse Mode (PIM-SM): Protocol Specification",
RFC 2362, June 1998.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, November 1997.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3973] Adams, A., Nicholas, J., and W. Siadak, "Protocol
Independent Multicast - Dense Mode (PIM-DM): Protocol
Specification (Revised)", RFC 3973, January 2005.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
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8.2. Informative references
[RFC2547] Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547,
March 1999.
[I-D.ietf-l3vpn-rfc2547bis]
Rosen, E., "BGP/MPLS IP VPNs",
draft-ietf-l3vpn-rfc2547bis-03 (work in progress),
October 2004.
[I-D.ietf-l3vpn-vpn-vr]
Knight, P., Ould-Brahim, H., and B. Gleeson, "Network
based IP VPN Architecture using Virtual Routers",
draft-ietf-l3vpn-vpn-vr-02 (work in progress), April 2004.
[I-D.ietf-ssm-arch]
Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", draft-ietf-ssm-arch-07 (work in progress),
October 2005.
[RFC2432] Dubray, K., "Terminology for IP Multicast Benchmarking",
RFC 2432, October 1998.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[I-D.ietf-mpls-rsvp-te-p2mp]
Aggarwal, R., "Extensions to RSVP-TE for Point to
Multipoint TE LSPs", draft-ietf-mpls-rsvp-te-p2mp-03 (work
in progress), October 2005.
[I-D.minei-wijnands-mpls-ldp-p2mp]
Minei, I., "Label Distribution Protocol Extensions for
Point-to-Multipoint and Multipoint-to-Multipoint Label
Switched Paths", draft-minei-wijnands-mpls-ldp-p2mp-00
(work in progress), October 2005.
[I-D.leroux-mpls-mp-ldp-reqs]
Roux, J., "Requirements for point-to-multipoint extensions
to the Label Distribution Protocol",
draft-leroux-mpls-mp-ldp-reqs-02 (work in progress),
October 2005.
[I-D.ietf-pim-bidir]
Handley, M., "Bi-directional Protocol Independent
Multicast (BIDIR-PIM)", draft-ietf-pim-bidir-08 (work in
progress), October 2005.
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[RFC1853] Simpson, W., "IP in IP Tunneling", RFC 1853, October 1995.
[RFC3353] Ooms, D., Sales, B., Livens, W., Acharya, A., Griffoul,
F., and F. Ansari, "Overview of IP Multicast in a Multi-
Protocol Label Switching (MPLS) Environment", RFC 3353,
August 2002.
[RFC3272] Awduche, D., Chiu, A., Elwalid, A., Widjaja, I., and X.
Xiao, "Overview and Principles of Internet Traffic
Engineering", RFC 3272, May 2002.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC4045] Bourdon, G., "Extensions to Support Efficient Carrying of
Multicast Traffic in Layer-2 Tunneling Protocol (L2TP)",
RFC 4045, April 2005.
[RFC3809] Nagarajan, A., "Generic Requirements for Provider
Provisioned Virtual Private Networks (PPVPN)", RFC 3809,
June 2004.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, July 1998.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
May 1998.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8",
BCP 53, RFC 3180, September 2001.
[RFC1157] Case, J., Fedor, M., Schoffstall, M., and J. Davin,
"Simple Network Management Protocol (SNMP)", STD 15,
RFC 1157, May 1990.
[I-D.ietf-mpls-lsp-ping]
Kompella, K. and G. Swallow, "Detecting MPLS Data Plane
Failures", draft-ietf-mpls-lsp-ping-12 (work in progress),
December 2005.
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[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[I-D.ietf-mpls-p2mp-lsp-ping]
Yasukawa, S., "Detecting Data Plane Failures in Point-to-
Multipoint MPLS Traffic Engineering - Extensions to LSP
Ping", draft-ietf-mpls-p2mp-lsp-ping-00 (work in
progress), September 2005.
[I-D.mathis-frag-harmful]
Mathis, M., "Fragmentation Considered Very Harmful",
draft-mathis-frag-harmful-00 (work in progress),
July 2004.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
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URIs
[3] <mailto:christian.jacquenet@francetelecom.com>
[4] <mailto:y.kamite@ntt.com>
[5] <mailto:jeanlouis.leroux@francetelecom.com>
[6] <mailto:nicolai.leymann@t-systems.com>
[7] <mailto:renaud.moignard@francetelecom.com>
[8] <mailto:thomas.morin@francetelecom.com>
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Appendix A. Requirements summary
This section is a summary of all requirements expressed as MUST or
SHOULD, proposed for quick reference.
Please keep in mind that the full text of corresponding sections is
the one reference, and refer to it to uncover any ambiguity in the
summaries below.
A.1. General Requirements (Section 3)
o SHOULD satisfy requirements documented in RFC4031 "Service
Requirements for Layer 3 Provider Provisioned Virtual Private
Networks (PPVPNs)"
o MUST interoperate seamlessly with current unicast solutions
A.2. Scalability orders of magnitude (Section 4.2)
A multicast VPN solution...
o SHOULD support a number of multicast VPNs ranging from one to
several thousands
o SHOULD support a number of multicast VPNs per PE of several
hundreds, and may have to scale up to thousands VPNs per PE
o SHOULD support a number of CEs per multicast VPN per PE going up
to several hundreds (and may target the support of thousands of
CEs)
o SHOULD support several hundreds of PEs per multicast VPN, and MAY
usefully scale up to thousands
o SHOULD support hundreds of source-connected-PEs per VPN, and some
deployment scenarios involving many-to-many applications, may
require supporting a number of source-connected-PEs equal to the
number of PEs (hundreds or thousands)
o SHOULD support hundreds or even thousands of streams sourced per
VPN
o SHOULD support hundreds of streams sourced per PE
A.3. Requirements from mutlicast VPN customer standpoint (Section 5.1)
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o Service definition
* the multicast service MUST be provider provisioned and SHALL
NOT require customer's devices (CE) to support any extra
feature compared to those required for multicast in a non-VPN
context
o CE-PE Protocols
* CEs and PEs SHOULD employ existing multicast protocols
* the support of PIM-SM (including SSM model) and IGMP is
REQUIRED
* Bidir-PIM support is RECOMMENDED
* when IPv6 is supported by a VPN solution, relevant IPv6
corresponding protocols SHOULD also be supported / MLD support
is REQUIRED for IPv6 implementations
o QoS Requirements
* the level of availability for the multicast service SHOULD be
on par with what exists for unicast traffic
* same traffic protection mechanisms SHOULD be available for
customer multicast traffic when it is carried over the service
provider's network.
* DiffServ mechanisms that include multicast traffic
identification, classification and marking capabilities, as
well as multicast traffic policing, scheduling and conditioning
capabilities, MUST be supported
* it is RECOMMENDED that a multicast VPN solution be designed
appropriately with regards to group join delay performance
* it SHOULD be possible to tune the multicast routing or group
management protocol used on the PE-CE adjacency to reduce the
group leave delay to the minimum
* a multicast VPN solution SHOULD as much as possible ensure that
client multicast packets are neither lost nor duplicated, even
when changes occur in the way a client multicast data stream is
carried over the provider network
* packet loss issues have to be considered when a new source
starts to send traffic to a group: any receiver interested in
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receiving such traffic SHOULD be serviced accordingly
o SLA Parameters measurements
* a multicast VPN solution MUST support SLA monitoring
capabilities
o Security Requirements
* a multicast VPN solution MUST provide an architecture with the
same level of security both for both unicast and multicast
traffic
* the activation of multicast features SHOULD be possible:
+ with a VRF or VR granularity
+ with a CE granularity (when multiple CE of a same VPN are
connected to a common VRF)
+ with a distinction between multicast reception and emission
+ with a multicast group and/or channel granularity
o Monitoring and troubleshooting
* a service provider and its customers MUST be able to manage the
capabilities and characteristics of their multicast VPN
services
* automated operations and interoperability with standard
management platforms SHOULD be supported
* the monitoring of multicast specific parameters and statistics
MUST include multicast traffic statistics: total traffic
conveyed, incoming, outgoing, dropped, etc., by period of time
* a multicast VPN solution SHOULD allow customers to find out
their current resource usage and to receive some kind of
feedback if their usage exceed bounds
o Extranet
* a multicast VPN solution MUST support deployments where VRFs or
VR are part of more than one multicast VPN
* a multicast VPN solution MUST offer means so that:
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+ receivers behind attached CEs can receive multicast traffic
sourced in any of the VPNs
+ sources behind attached CEs can reach multicast traffic
receivers located in any of the VPNs
+ multicast can be independently enabled for the different
VPNs
* support for this feature SHOULD not require replicating
multicast traffic on a PE-CE link
o Carrier's carrier
* A multicast VPN solution SHOULD support the carrier's carrier
model in a scalable and efficient manner
* the protocols that may be used at the PE-CE level SHOULD NOT be
restricted to protocols required as per Section 5.1.2 (CE-PE
Multicast routing and management protocols) and SHOULD include
some of the protocols listed in Section 5.2.3 (Tunneling
Requirements)
* in the context of MPLS-based L3VPN deployments, some MPLS label
distribution SHOULD happen at the PE-CE level
o Multihoming
* a multicast VPN solution SHOULD be able to offer multi-homing,
CE-PE link load balancing and failover
* a multicast VPN solution SHOULD support redundant topology of
CE-PE links
* a multicast VPN solution SHOULD minimize multicast traffic
disruption and failover
* if the customer uses some control mechanism for RP redundancy
on PIM-SM (e.g. BSR), it SHOULD work transparently through
that VPN
o RP Engineering
* a multicast VPN solution SHOULD propose a way to help on
solving the RP engineering issue in a VPN context
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o Addressing
* a multicast VPN solution SHOULD NOT impose restrictions on
multicast group addresses used by VPN customers
* an overlap of multicast group address sets used by different
VPN customers MUST be supported
* the use of globally unique means of multicast-based service
identification at the scale of the domain where such services
are provided SHOULD be recommended
o Minimum MTU
* a multicast VPN solution SHOULD let customers' devices be free
of any fragmentation or reassembly activity
* a committed minimum path MTU size SHOULD be provided to
customers
* a minimum 1500 bytes IP MTU SHOULD be provided
* a multicast VPN solution SHOULD also be compatible with Path
MTU discovery mechanisms
A.4. Requirements from provider standpoint
o Scalability
* solutions MUST be designed to scale well with an increase in
the number of any of the following:
+ the number of PEs
+ the number of customers VPNs (total and per PE)
+ the number of PEs and sites in any VPN
+ the number of client multicast channels (groups or source-
groups)
* scalability of both performance and operation MUST be
considered
* key considerations SHOULD include:
+ the processing resources required by the control plane
(neighborhood or session maintenance messages, keep-alives,
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timers, etc.)
+ the memory resources needed for the control plane
+ the amount of protocol information transmitted to manage a
multicast VPN (e.g. signalling throughput)
+ the amount of control plane processing required on PE and P
to add remove a customer site (or a customer from a
multicast session)
+ the number of multicast IP addresses used (if IP multicast
in ASM mode is proposed as a multicast distribution tunnel)
+ other particular elements inherent to each solution that
impacts scalability (e.g., if a solution uses some
distribution tree inside the core, topology of the tree and
number of leaf nodes may be some of them)
* solutions SHOULD offer the possibility of sharing core
resources between different multicast streams
o Resource optimization
* a multicast VPN solution SHOULD offer the service providers
appropriate configuration settings that let them tune the
bandwidth/state trade-off according to their peculiar
constraints
o Traffic Engineering
* a multicast VPN solution supporting TE for unicast traffic
SHOULD also be able to provide traffic engineering features for
the MDTunnels
* a solution SHOULD offer means to support key TE objectives as
defined in RFC3272 "Overview and Principles of Internet Traffic
Engineering"
o Tunnelling
* a multicast VPN solution SHOULD be designed so that control and
forwarding planes are not inter-dependent
* the control plane SHALL NOT depend on which forwarding plane is
used (and vice versa)
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* the choice of forwarding plane SHOULD NOT be limited by the
design of the solution
* solution SHOULD also NOT be tied to a specific tunneling
technology
* a multicast VPN solution extending a unicast L3 PPVPN solution,
consistency in the tunneling technology has to be privileged:
such a solution SHOULD allow the use of the same tunneling
technology for multicast as for unicast
* a solution SHOULD be able to use a range of tunneling
technologies for MDTunnels, including point-to-point and point-
to-multipoint, such as [please refer to section Section 5.2.3]
* it is RECOMMENDED that a solution is built so that it can use
the point to multipoint variants of these techniques
* a solution SHOULD support a method that provides the minimum
path MTU of the MDTunnel
o Control mechanisms
* a solution MUST provide some mechanisms to control the sources
within a VPN
* a solution MUST provide mechanisms to control the number of
multicast groups or channels VPN users are entitled to
subscribe to and/or the total bit rate represented by the
corresponding multicast traffic
* all these mechanisms MUST be configurable by the service
provider in order to control the amount of multicast traffic
and state within a VPN
o Inter-As, inter-provider
* a multicast VPN solution MUST support inter-AS VPNs
* a multicast VPN solution SHOULD support inter-provider VPNs
* a multicast VPN solution SHOULD provide inter-AS mechanisms
requiring the least possible coordination between providers
* 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
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* if a solution does require a single tunnel to span P routers in
multiple ASs, the solution SHOULD provide mechanisms to ensure
that the inter-provider co-ordination to setup such a tunnel is
minimized
* such support SHOULD be possible without compromising other
requirements expressed in this requirement document, and SHALL
NOT incur penalty on scalability and bandwidth usage
o QoS differentiation
* a multicast VPN solution SHOULD give a provider the ability to
offer, guarantee and enforce differentiated levels of QoS for
different customers.
o Infrastructure security
* some mechanism SHOULD be proposed so that the frequency of
changes in the way client traffic is carried over the core can
be bounded
* a multicast VPN solution SHOULD whether avoid single points of
failures or propose some technical solution making possible to
implement a failover mechanism
* it is RECOMMENDED that a multicast VPN solution support means
to ensure the integrity and authenticity of multicast-related
exchanges across inter-ASes or inter-provider borders
o Robustness
* a multicast VPN solution SHOULD whether avoid single points of
failures or propose some technical solution making possible to
implement a failover mechanism
o Management tools, OAM
* automatic configuration and discovery SHOULD be prioritized
* monitoring of multicast specific parameters and statistics
SHOULD be offered to the service provider
* the provider SHOULD have access to:
+ multicast traffic statistics
+ IP Performance Metrics-related information that is relevant
to the multicast traffic usage
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+ alarms when limits are reached
+ statistics on parameters that could help the provider to
evaluate its optimality/state trade-off
* this information SHOULD be made available through standardized
SNMP
o Compatibility and migration issues
* unicast and multicast services MUST be able to co-exist within
the same VPN
* the introduction of IP multicast VPN capabilities in devices
that participate to the deployment and the maintenance of a
multicast VPN SHOULD be as smooth as possible
* a multicast VPN solution SHOULD prevent compatibility and
migration issues
* it SHOULD be an aim of any multicast VPN solution to offer as
much backward compatibility as possible
* a solution SHOULD state a migration policy from possibly
existing deployments
o Troubleshooting
* a multicast VPN solution SHOULD provide monitoring information
describing how client traffic is carried over the network
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Appendix B. Changelog
This section lists changes made to this document (minor or editorial
changes excepted) between major revisions.
It shall be removed before publication as an RFC.
B.1. Changes between -00 and -01
o integrated comments made on L3VPN WG mailing list after -00
submission
o completed Carrier's carrier section (5.1.9)
o updates in sections 5.1 and 5.2 about minimum MTU
o added a section about "Quality of Service Differentiation" as ISP
requirement (section 5.2.5)
o added P2MP LDP extensions as possible MDTunnels techniques
(section 5.2.3.1)
o started to build section 4 "Use Case"
o detailed section 5.1.3 "QoS", most notably about group join and
leave delays
o additions to section 5.2.12 "Inter-AS, inter-provider"
o added MDTunnel verification requirement to section 5.2.11
o moved "Architectural Considerations" section
o moved contributors to top of document
o made draft content agnostic to unicast L3VPN solutions
o added two appendixes: "Changelog" and "Requirement summary"
o conversion to XML [RFC2629] with the help of some scripting and
Bill Fenner's xml2rfc XMLMind plugin
o lot's of editorial changes
B.2. Changes between -01 and -02
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o based on survey results:
* restructure use case scenario section
* fill in Scalability orders of magnitude section
* better detail requirements for protocols at the PE-CE level
* add considerations about PEs with scarce connectivity to
section 5.2.2.3
* step up requirement level for Extranet (Section 5.1.7)
o some editorial changes
o use capitalized wording for some requirements
o fill in requirements summary (Appendix A)
B.3. Changes between -02 and -03
o made inter-AS a MUST (and moved the whole section up)
o add a requirement about security of multicast-related exchanges
across providers/ASes, in Section 5.2.7
o some editorial changes and fixed typos
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Author's Address
Thomas Morin (editor)
France Telecom R&D
2, avenue Pierre Marzin
Lannion 22307
France
Email: thomas.morin@rd.francetelecom.com
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http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
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this standard. Please address the information to the IETF at
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Disclaimer of Validity
This document and the information contained herein are provided on an
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
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