L3VPN Working Group T. Morin, Ed. Internet Draft France Telecom R&D Category: Informational February 2005 Requirements for Multicast in L3 Provider-Provisioned VPNs Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 3 of RFC3667 [RFC3667]. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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 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 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 l3vpn@ietf.org. The charter for l3vpn may be found at http://www.ietf.org/html.charters/l3vpn-charter.html 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. Morin et al. Informational - Expires August 2005 [Page 1] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 Table of Contents 1. Introduction...............................................3 2. Conventions used in this document..........................3 2.1. Terminology................................................3 2.2. Conventions................................................4 3. Problem Statement..........................................5 3.1. Motivations................................................5 3.2. General Requirements.......................................5 3.3. Scalability vs. Optimality.................................5 4. Use cases..................................................6 5. Requirements for supporting IP multicast within L3 PPVPNs..6 5.1. End user/customer standpoint...............................6 5.1.1. Service definition.........................................6 5.1.2. CE-PE Multicast routing and management protocols...........6 5.1.3. Quality of Service (QoS)...................................6 5.1.4. SLA parameters measurement.................................7 5.1.5. Security Requirements......................................8 5.1.6. Monitoring and Troubleshooting.............................8 5.1.7. Extranet...................................................9 5.1.8. Internet Multicast.........................................9 5.1.9. Carrier's carrier..........................................9 5.1.10. Multi-homing, load balancing and resiliency................9 5.1.11. RP Engineering............................................10 5.1.12. Addressing................................................10 5.1.13. Fragmentation.............................................10 5.2. Service provider standpoint...............................11 5.2.1. Scalability...............................................11 5.2.2. Resource optimization.....................................12 5.2.3. Tunneling Requirements....................................13 5.2.4. Control mechanisms........................................14 5.2.5. Infrastructure security...................................14 5.2.6. Robustness................................................15 5.2.7. Management tools, OAM.....................................15 5.2.8. Compatibility and migration issues........................16 5.2.9. Troubleshooting...........................................16 5.2.10. Inter-AS, inter-provider..................................16 5.2.11. Architectural Considerations..............................17 6. Security Considerations...................................17 7. Acknowledgments...........................................17 8. References................................................17 8.1. Normative references......................................17 8.2. Informative references....................................18 9. Contributors..............................................19 10. Editor's addresses........................................19 11. Intellectual Property Notice..............................20 Morin et al. Informational - Expires August 2005 [Page 2] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 1. Introduction VPN services satisfying requirement defined in [VPN-REQ] are now being offered by many service providers worldwide. The success of those VPN services is due to intrinsic characteristics of the solutions: - Customers are unaware of the deployed network technology and do not need to activate specific mechanisms to support traffic being carried across L3VPN services, - P-routers in the core do not need to be explicitly aware of the L3VPN services which allows the P-routers to remain unaware of the number of VPN customers and so facilitates scalability, - Operator's configuration actions when adding new customers are minimized by the dynamic configuration of the VPNs. 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 PP IP VPN solutions. A simple solution to support multicast-based services in L3 PPVPNs consists in establishing unicast tunnels across the core network, and replicating traffic on PEs. Such a technique, despite the advantage of keeping the core unaware of multicast- specific issues has obvious drawbacks, which include scalability issues, operational costs, and bandwidth usage. This document complements the generic L3 VPN requirement document [VPN-REQ], 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. 2. Conventions used in this document 2.1. Terminology Although the reader is assumed to be familiar with the terminology defined in [VPN-REQ], [RFC2547bis], [PIM-SM], [PIM-SSM] the following glossary of terms may be worthwhile. Morin et al. Informational - Expires August 2005 [Page 3] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 Moreover we also propose here generic terms for concept that naturally appears when multicast in VPNs is discussed. Please refer to the [PPVPN-TERM] document for details about terminology specifically relevant to VPN aspects. - ASM: Any Source Multicast. One of the two multicast service models that denotes the source/receiver heuristic. - Multicast-enabled VPN: a VPN which supports IP multicast capabilities, i.e. whose 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 [PPVPN-TERM] - 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). - 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] and [bidir-PIM]) 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 RFC 2119 [RFC2119]. Morin et al. Informational - Expires August 2005 [Page 4] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 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, it 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 [VPN-REQ]: 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] or [VR]) and retain consistency with those, although this is not a core requirement. 3.3. Scalability vs. Optimality When transporting multicast VPN traffic over a service provider network, there intrinsically is tension between resource optimization and minimizing the number of protocol states maintained. Thus, some trade-off has to be made, and this document will express some requirements related to this trade-off. Morin et al. Informational - Expires August 2005 [Page 5] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 4. Use cases This section aims at presenting a few representative examples of multicast deployments in a VPN context. The goal is to highlight how different applications and network contexts may have a different impact on how a trade-off is made. [to be completed] 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", a solution that allows to perform multicast in an L3 provider provisioned VPN, 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 the customer's devices (CE) to support some extra features. 5.1.2. CE-PE Multicast routing and management protocols Consequently to section 3.1, the CEs and PEs SHOULD be able to operate existing multicast protocols. Such protocols SHOULD include : PIM-SM [PIM-SM] (including PIM-SSM [PIM-SSM], and bidirectional PIM [BIDIR-PIM]), PIM-DM [PIM-DM], and IGMP (v1, v2 and v3 [IGMPv1] [IGMPv2] [IGMPv3]). Among those protocols, PIM-SM is considered a MUST. When IPv6 is supported by a VPN solution, the Multicast Listener Discovery Protocol (MLD) SHOULD also be supported (v1, v2 [MLD] [MLDv2]). 5.1.3. Quality of Service (QoS) First, general considerations about QoS in L3 VPNs as developed in section 5.5 of [VPN-REQ] are also relevant to this section. QoS includes various parameters such as delay, jitter, packet loss, and service availability expressed in percentage of time. These Morin et al. Informational - Expires August 2005 [Page 6] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 parameters are already defined for the current unicast provider provider-provisioned VPN services, are sold by the service provider to the customers and defined in the SLA (Service Level Agreements). 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. 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 call admission control. Moreover, 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: any receiver interested in receiving such traffic SHOULD be serviced accordingly. 5.1.4. SLA parameters measurement As 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, delay and latency time (time to start receiving a multicast group traffic across the VPN). A generic discussion of SLAs is provided in [PPVPN-GR]. Morin et al. Informational - Expires August 2005 [Page 7] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 5.1.5. Security Requirements Security is a key point for a customer who uses subscribes to a VPN service. The RFC2547 model [RFC2547bis] offers some guarantees concerning the security level of data transmission within the VPN. A multicast VPN solution MUST provide an architecture that can provide the same level of security both for both the unicast and multicast traffics. Moreover, the activation of multicast features SHOULD be possible: - with a VRF 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 A multicast VPN solution may choose to make the optimality/scal- ability 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 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 : - multicast traffic statistics: total traffic conveyed, incoming, outgoing, dropped, etc., by period of time (as a MUST) - 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 Morin et al. Informational - Expires August 2005 [Page 8] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 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. The need for a corresponding multicast feature will need to be assessed in further revisions of this document. If this is the case, a multicast solution SHOULD offer means so that: - receivers behind attached CEs can receive multicast traffic sourced in any of the VPNs (if security policy permits) - sources behind attached CEs can reach multicast traffic receivers located in any of the VPNs - 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, an enterprise using a multicast-enabled VPN should be able to receive multicast streams sent by a source in another VPN, and should also be able to be a source for a multicast stream towards another VPN. In any case a solution not supporting such a feature MUST be compatible with setups where a VRF is part of multiple VPNs and MUST document how it operates on multicast traffic in such a context. 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 This issue is to be examined in a further revision. 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 Morin et al. Informational - Expires August 2005 [Page 9] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 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 inside the VPN, and of globally assigned group addresses for services for which traffic may be transmitted outside the VPN (e.g. GLOP [GLOP]). 5.1.13. Fragmentation 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, VPN multicast solution SHOULD consider the control and management of MTU, especially independently from of unicast. Morin et al. Informational - Expires August 2005 [Page 10] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 Any tunneling mode used to carry multicast VPN customer traffic MUST properly handle fragmentation, and permit proper path MTU discovery for multicast traffic. 5.2. Service provider standpoint Note: please remember that, to avoid repetition and confusion with terms used in solution draft, 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] model, a P-router sees a number of MPLS tunnels that is only linked to the number of PEs and not to the number of customers. 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. 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: - 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, timers, etc.) - the memory resources needed for the control plane Morin et al. Informational - Expires August 2005 [Page 11] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 - the amount of protocol information transmitted to manage a multicast VPN (e.g. signaling 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) It is expected that the applicability of each solution will be evaluated with regards to the aforementioned scalability criteria. 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, and that the most sensible approach is a versatile solution offering the service providers appropriate configuration settings that let them tune the trade-off according to their peculiar Morin et al. Informational - Expires August 2005 [Page 12] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 constraints (network topology, platforms, customer applications, level of service offered etc.). As an illustration here are some example bounds of the tradeoff space: - Bandwidth optimization: setting up somehow optimal core MDTunnels whose topology (PIM tree or P2MP LSP, etc.) whose topology precisely follows customer's multicast routing. 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 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 [RFC 3272], 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. 5.2.3. Tunneling Requirements 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. Migration and operations ease are the main motivations behind this requirement. Morin et al. Informational - Expires August 2005 [Page 13] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 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 L2TP (including L2TP for multicast [L2TP-MCAST]), IPsec [IPSEC], GRE [GRE] (including GRE in multicast IP trees), IP-in-IP, MPLS (including P2MP [P2MP]), etc. Naturally, using the point-to-multipoint variants mentioned here may help improve bandwidth use in our multicast VPN context. 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. 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. 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. Moreover, since multicast traffic and routing are intrinsically dynamic (receiver-initiated), some mechanism must be proposed so that the frequency of changes in the way client traffic is carried over the core is 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 Morin et al. Informational - Expires August 2005 [Page 14] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 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. Last, control mechanisms described in previous section are also to be considered from this infrastructure security point of view. 5.2.6. Robustness Resiliency is also crucial to infrastructure security, thus a multicast VPN solution shall whether avoid single points of failures or propose some technical solution making possible to implement a failover 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. 5.2.7. Management tools, OAM The operation of a multicast VPN solution SHALL be as light as possible and providing automatic configuration and discovery SHOULD 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: - Multicast traffic statistics (total traffic conveyed, incoming, outgoing, dropped, etc., by period of time) - Information about client multicast resource usage (state and throughput) - 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. - 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") Morin et al. Informational - Expires August 2005 [Page 15] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 - 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). 5.2.8. 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 capabilities in devices that participate to the deployment and the maintenance of a 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 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 into VPN solution to offer as much backward compatibility as possible. Ideally, although improbable, would be the ability to offer multicast VPN services across a network containing some legacy routers not supporting multicast VPN specific features. 5.2.9. 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. Depending on the implementation such verification could be initiated by source-PE or receiver-PE. 5.2.10. Inter-AS, inter-provider Morin et al. Informational - Expires August 2005 [Page 16] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 A multicast VPN solution SHOULD support inter-AS and inter inter- provider VPNs. Considerations about coexistence with unicast inter- AS VPN Options A, B and C (as described in section 10 of [RFC2547bis]) are strongly encouraged. Moreover such support should be possible without compromising other requirements expressed in this requirement document, and should not incur penalty on scalability and bandwidth resource usage. 5.2.11. 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. 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 sections 4.2.4 and 4.1.5. 7. Acknowledgments The authors would like to thank Vincent Parfait (Equant), Zubair Ahmad (Equant), Elodie Hemon-Larreur, Sebastien Loye (France Telecom), Rahul Aggarwal (Juniper), Hitoshi Fukuda (NTT Communications), Adrian Farrel, Daniel King, for their review, valuable input and feedback. 8. References 8.1. Normative references [RFC3667] S.Bradner, "IETF Rights in Contributions", BCP 78, RFC 3667, February 2004. [RFC3668] S.Bradner, Ed., "Intellectual Property Rights in IETF Technology", BCP 79, RFC 3668, February 2004. [RFC2026] S. Bradner, "The Internet Standards Process - Revision 3", BCP 9, RFC 2026, October 1996. [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [VPN-REQ] M. Carugi, et. al., "Service requirements for Layer 3 PPVPNs", draft-ietf-l3vpn-requirements-02 (work in progress) Morin et al. Informational - Expires August 2005 [Page 17] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 [PIM-SM] D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S. Deering, M. Handley, V. Jacobson, C. Liu, P. Sharma, L. Wei, "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification.", RFC 2362, June 1998. [IGMPv1] S. Deering, "Host extensions for IP multicasting", RFC 1112 [IGMPv2] W. Fenner, "Internet Group Management Protocol, IGMP version 2", RFC 2236, November 1997. [IGMPv3] B. Cain, "Internet Group Management Protocol, Version 3", RFC 3376 8.2. Informative references [RFC2547bis] E. Rosen, Y. Rekhter "BGP/MPLS VPNs", draft-ietf-l3vpn- rfc2547bis-03 (work in progress), October 2004 [VR] P. Knight et al., "Network based IP VPN Architecture using Virtual Routers", August 2004, draft-ietf-l3vpn-vpn-vr-02 (work in progress) [PIM-SSM] H. Holbrook, B. Cain, "Source-Specific Multicast for IP" September 2004, draft-ietf-ssm-arch-06 (work in progress) [BIDIR-PIM] Mark Handley, Isidor Kouvelas, Tony Speakman, Lorenzo Vicisano "Bi-directional Protocol Independent Multicast", July 2004, draft-ietf-pim-bidir-07 (work in progress) [IPMCAST-MPLS] D. Ooms, B. Sales, W. Livens, A. Acharya, F. Griffoul and F. Ansari, "Overview of IP Multicast in a Multi-Protocol Label Switching (MPLS) Environment", RFC3353, August 2002. [P2MP] R. Aggarwal, D. Papadimitriou, S. Yasukawa, "Extended RSVP-TE for Point-to-Multipoint LSP Tunnels", July 2004, draft- yasukawa-mpls-rsvp-p2mp-04 (work in progress) [L2TP-MCAST] G. Bourdon, "Extensions to support efficient carrying of multicast traffic in Layer-2 Tunneling Protocol (L2TP)", draft- ietf-l2tpext-mcast-05 (work in progress) [RFC2365] Meyer, D., ôAdministratively Scoped IP Multicastö, RFC 2365, July 1998. [RFC2330] Paxson, V. et al., "Framework for IP Performance Metrics", RFC 2330, May 1998. [RFC2475] Blake, S., et al., ôAn Architecture for Differentiated Serviceö, RFC 2475, December 1998. Morin et al. Informational - Expires August 2005 [Page 18] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 [PPVPN-TERM] L. Anderssoo, T. Madsen, "Provider Provisioned VPN terminology", draft-ietf-l3vpn-ppvpn-terminology-04, September 2004 [GRE] [IP-in-IP] [GLOP] D. Meyer, P. Lothberg "Addressing in 233/8", RFC2770, February 2000 [SNMP] J. Case et. al, "A Simple Network Management Protocol (SNMP)", RFC1157, May 1990 9. Contributors Contributors are listed in alphabetical order. Christian Jacquenet France Telecom 3, avenue Francois Chateau CS 36901 35069 RENNES Cedex Email: christian.jacquenet@francetelecom.com 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 Jean-Louis Le Roux France Telecom R & D 2, avenue Pierre-Marzin 22307 Lannion Cedex France Email: jeanlouis.leroux@francetelecom.com Renaud Moignard France Telecom R & D 2, avenue Pierre-Marzin 22307 Lannion Cedex France Email: renaud.moignard@francetelecom.com 10. Editor's addresses Thomas Morin France Telecom R & D 2, avenue Pierre-Marzin Morin et al. Informational - Expires August 2005 [Page 19] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 22307 Lannion Cedex France Email: thomas.morin@francetelecom.com 11. 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Full Copyright Statement "Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. Morin et al. Informational - Expires August 2005 [Page 20] Internet Draft Requirements for multicast in L3 PPVPNs February 2005 This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Morin et al. Informational - Expires August 2005 [Page 21]