BEHAVE WG C. Jacquenet Internet-Draft M. Boucadair Intended status: Informational France Telecom Expires: September 8, 2011 Y. Lee Comcast J. Qin ZTE T. Tsou Huawei Technologies (USA) March 07, 2011 IPv4-IPv6 Multicast: Problem Statement and Use Cases draft-jaclee-behave-v4v6-mcast-ps-00 Abstract This document discusses issues and requirements raised by IPv4-IPv6 multicast interconnection and co-existence scenarios. It also presents the various multicast use cases which may happen during IPv6 transitioning. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 8, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the Jacquenet, et al. Expires September 8, 2011 [Page 1] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. Context . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Dual-Stack Multicast Delivery Infrastructure . . . . . . . 8 3.4. Mono-Stack Multicast Delivery Infrastructure . . . . . . . 9 3.4.1. Translation Cases . . . . . . . . . . . . . . . . . . 11 3.4.2. Traversal Cases . . . . . . . . . . . . . . . . . . . 12 4. Issues and Required Functions . . . . . . . . . . . . . . . . 15 4.1. Fast Zapping . . . . . . . . . . . . . . . . . . . . . . . 15 4.2. Group and Source Discovery Considerations . . . . . . . . 15 4.3. Subscription . . . . . . . . . . . . . . . . . . . . . . . 16 4.4. Multicast Tree Computation . . . . . . . . . . . . . . . . 16 4.5. SLA Considerations . . . . . . . . . . . . . . . . . . . . 16 4.6. Load Balancing . . . . . . . . . . . . . . . . . . . . . . 16 4.7. Bandwidth Consumption . . . . . . . . . . . . . . . . . . 17 4.8. ASM-SSM Considerations . . . . . . . . . . . . . . . . . . 17 4.9. Interconnection Functions . . . . . . . . . . . . . . . . 17 4.9.1. Interworking Functions for Control Flows . . . . . . . 17 4.9.2. Interconnection Function for Traffic Flows . . . . . . 18 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 18 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 8.1. Normative References . . . . . . . . . . . . . . . . . . . 19 8.2. Informative References . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 Jacquenet, et al. Expires September 8, 2011 [Page 2] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 1. Introduction In current operational deployments, IP multicast forwarding scheme is used by many service providers to deliver Live TV broadcasting services. Numerous players intervene in the delivery of this service: (1) Content providers: the content can be provided by the same provider as the one providing the connectivity service or by distinct providers (e.g., external paid channels); (2) Network provider: is responsible for carrying multicast flows from head-ends to receivers. During the transition of multicast to IPv6, there will be various issues encountered and requirements raised correspondingly. The requirement of service continuity should be an essential one which may include: the access to legacy contents (IPv4 framed) from receivers is still available where if the assignment of a dedicated global IPv4 address to the receiver is not possible anymore or even after the receivers are migrated to IPv6 and; the delivery of new contents (IPv6 framed) to legacy receivers is also possible and; in cases where if underlying transport network(s) is of different address family than that of the source and/or receivers, the delivery of multicast data is still available (e.g., in the context of DS-Lite deployment, the network has been firstly upgraded to IPv6 while the source and receivers are not). This document does make any assumption on the techniques used for the delivery of multicast services (e.g., native IP multicast with or without traffic isolation features, use of P2MP RSVP-TE, P2MP mLDP LSPs, mVPN, etc. ). This document further elaborates on the context and discusses multicast-inferred issues and requirements. 1.1. Goals The goal is to clarify the problem space and get a general consent of the objectives. In particular, the ambition is to provide answers to: o What are the hurdles encountered for the delivery of multicast- based service offering when both IPv4 and IPv6 co-exist? o What standardization effort is needed: is there any missing function and protocol extensions? o Check if both encapsulation and translation schemes are concerned. Jacquenet, et al. Expires September 8, 2011 [Page 3] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 1.2. Terminology This document uses the following terms: o Multicast Source: Source, in short o Multicast Receiver: Receiver, in short, e.g.- STB o Multicast Delivery Network: Network in short, covers the realm from DR device (directly connected to the Source) to IGMP/MLD Querier device (directly connected to the Receiver). 2. Discussion Global IPv4 address depletion inevitably challenges service providers who must guarantee IPv4 service continuity during the forthcoming transition period. In particular, access to IPv4 contents that are multicast to IPv4 receivers becomes an issue when the forwarding of multicast data assumes the use of global IPv4 addresses. The rarefaction of global IPv4 addresses may indeed affect the multicast delivery of IPv4-formatted contents to IPv4 receivers. For example, the observed evolution of access infrastructures from a service-specific, multi-PVC scheme towards a "service-agnostic", single PVC scheme, assumes the allocation of a globally unique IPv4 address on the WAN interface of the CPE (or to a mobile terminal), whatever the number and the nature of the services the customer has subscribed to. During the transition period, the usage of the remaining global IPv4 address blocks will have to be rationalized for the sake of IPv4 service continuity. The current state-of-the-art suggests the introduction of NAT capabilities (generally denoted as CGN, for Carrier-Grade NAT) in providers networks, so that global IPv4 addresses will be shared between several customers. As a consequence, CPE or mobile UE devices will not be assigned a dedicated global IPv4 address anymore, and IPv4 traffic will be privately-addressed until it reaches one of the NAT capabilities deployed in the network. From a multicast delivery standpoint, this situation suggests the following considerations: o The current design of some multicast-based services like TV broadcasting often assumes that IPv4 multicast forwarding relies upon the use of a private IPv4 addressing scheme because of a walled garden approach. Privately-addressed IGMP [RFC2236] [RFC3376] traffic sent by IPv4 receivers is generally forwarded over a specific (e.g. "IP TV") PVC towards an IGMP Querier Jacquenet, et al. Expires September 8, 2011 [Page 4] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 located in the access infrastructure, e.g.- hosted by a BRAS device that is the PPP session endpoint and which may also act as a PIM DR [RFC4601] router. This design does not suffer from global IPv4 address depletion by definition. But it will be questioned when migrating the access infrastructure towards a publicly-addressed single PVC design scheme. o The progressive introduction of IPv6 as the only perennial solution to global IPv4 address depletion does not necessarily assume that multicast-based IPv4 services will be migrated accordingly. Access to IPv4 multicast contents raises several issues: (1) The completion of the IGMP-based multicast group subscription procedure, (2) The computation of the IPv4 multicast distribution tree, and (3) The IPv4-inferred addressing scheme to be used in a networking environment which will progressively become IPv6-enabled, but not necessarily IPv6 multicast enabled. o In any case, contents should not be multicast twice (using both versions of IP) for the sake of bandwidth optimization. Injecting multicast content using both IPv4 and IPv6 raises some dimensioning issues that should be carefully evaluated by service providers during network planning. For instance, if only few IPv6- enabled receivers are in use, it can be more convenient to convey multicast traffic over IPv4 rather than doubling the consumed resources for few users. There are at least several options that can deal with the aforementioned considerations. 1. Stick to a walled garden design that relies upon a private IPv4 addressing scheme. But this approach jeopardizes the evolution of access networking infrastructures towards the use of a unique, per-customer, globally-addressed, service-wise PVC design scheme. And it also delays migration towards IPv6 instead of encouraging it. 2. Use AMT (Automatic Multicast without explicit Tunnels, [I-D.ietf-mboned-auto-multicast]), to encapsulate IGMP traffic into UDP packets that will be sent to an AMT Relay located upstream in the network. This approach may not be suitable for the delivery of IP TV content in operational networks mainly due to delays which may be experienced for zapping. Note that unicast IP addresses are used for communicating with service platforms to get control information (e.g., channel lists) and, as the identification of customers for management, traffic engineering, etc. Jacquenet, et al. Expires September 8, 2011 [Page 5] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 The following sections elaborate more on the use cases, issues and requirements. 3. Use Cases 3.1. Purpose This section describes a set of use cases which need to be considered. As mentioned above, the walled garden scheme where private IPv4 addresses are used for the delivery of multicast-based service offerings is out of scope. 3.2. Context During transitioning, there might be a mix of multicast receivers, sources, and networks running in different address families. However, the operator should continue to deliver the multicast service to both IPv4 and IPv6 receivers. Since there is mis-match of IP address family of sources, receiver, and delivery network, the operator should plan carefully and choose the right transition technique that could efficiently utilize the network resources to deliver the services. Both fixed (Figure 1) and mobile networks (Figure 2, which reflects the current status of the IPv6 Study Item conducted within 3GPP and some public plans for the LTE deployment) have been considered. Jacquenet, et al. Expires September 8, 2011 [Page 6] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 +------------+-----------+-------------+-----------+----------------+ | Deployment | Legacy | CPE | Legacy | Underlying IP | | Model | Receiver | | Source | capabilities | +------------+-----------+-------------+-----------+----------------+ | DS | IPv4-only | IPv4-only | IPv4-only | IPv4 and IPv6 | | | | and DS | | | +------------+-----------+-------------+-----------+----------------+ | DS-Lite | IPv4-only | IPv4-only | IPv4-only | IPv4 and IPv6 | | | | and DS-Lite | | | +------------+-----------+-------------+-----------+----------------+ | Greenfield | -- | IPv6-only | --- | IPv6 | | IPv6 | | | | | +------------+-----------+-------------+-----------+----------------+ | Hybrid | IPv4-only | IPv4-only, | IPv4-only | IPv4 and IPv6 | | (*) | | DS and | | | | | | DS-Lite | | | +------------+-----------+-------------+-----------+----------------+ (*) Hybrid is used to denote a network where customers may be IPv4-only DS and/or DS-Lite serviced. Figure 1: IPv6 integration scenarios in fixed networks. +----------------+-----------+---------------+--------------------+ |Deployment Model| Legacy UE | Legacy source |Network Capabilities| +----------------+-----------+---------------+--------------------+ | DS PDP | IPv4-only | IPv4-only | IPv4 and IPv6 | +----------------+-----------+---------------+--------------------+ |IPv6-only PDP | IPv4-only | IPv4-only | IPv4 and IPv6(*) | +----------------+-----------+---------------+--------------------+ (*) The underlying network is likely to be dual-stack except for IPv6 greenfield deployments. Figure 2: IPv6 integration scenarios in mobile networks (PDP Activation). There are three variables to be considered when analyzing the multicast use cases, "Source", "Receiver" and the "Multicast Delivery Infrastructure" (denoted for short as "Network"). To simplify the analysis, one of the variables: "Network", is hold. So based on the capabilities of the underlying multicast delivery infrastructure. According to the above figures, two use cases can be considered: Jacquenet, et al. Expires September 8, 2011 [Page 7] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 o Dual-Stack: Both IPv4 and IPv6 multicast delivery function are wholly enabled; o Mono-Stack: Not wholly dual-stack enabled but for example, is either IPv4-only or IPv6-only, or may be a hybrid of IPv4 portion and IPv6 portion (refer to Hybrid cases in Figure 5). 3.3. Dual-Stack Multicast Delivery Infrastructure Dual-stack model is supposed to be the most straight forward deployment model where the network is dual-stack and the same content is sourced into both IPv4 and IPv6 multicast stream. Depending on the receiver, it could choose to listen to either stream. [NOTE: if the source is framed in single stack (i.e., IPv4-only or IPv6-only) or the network is not wholly dual-stack enabled, even there are both IPv4 and IPv6 receivers, it should not be regarded as the Dual-Stack Model use case. In this case, since the stream from source to receivers of the same address family can be natively delivered without any new functions, the native delivery portion is not taken into account. Then this is regarded as one of Mono-Stack Model cases. For example, the case where the source is IPv4 framed while the network is wholly dual-stack enabled and there are both IPv4 and IPv6 receivers, is simply regarded as the Case 1 in Mono-Stack Model; Or for example, the case where the source and receivers are dual-stack, and the network is IPv6-only, is regarded as Case 6, also refer to Section 3.4.2.] This model assumes the multicast content and delivery infrastructure is dual-stack. This assumption may not be valid because the dual- stack formatted source may not always be available since numerous players intervene in the delivery of multicast-based service: content providers and the network provider. The content may not be controlled by the underlying network providers. For this scenario, legacy IPv4 receivers will continue to access to IPv4-formatted multicast content. Figure 3 summarizes the issues encountered if this option is used. Jacquenet, et al. Expires September 8, 2011 [Page 8] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 +-----------------+----------------------------------------------+ | Deployment Model| Comments | +-----------------+----------------------------------------------+ | DS | No issue is encountered | +-----------------+----------------------------------------------+ | DS-Lite | For IPv4-only receivers, extra functions are | | | required to deliver the multicast service | +-----------------+----------------------------------------------+ | Hybrid | Idem as per DS-Lite case | +-----------------+----------------------------------------------+ Figure 3: Impact analysis. From a bandwidth perspective, it is not viable to duplicate the same content in IPv4 and IPv6. Indeed, injecting multicast content using both IPv4 and IPv6 raises dimensioning issues that should be carefully evaluated by service providers (in particular in the access network). For instance, if only few IPv6-enabled receivers are in use, it is more convenient to convey multicast traffic over IPv4 rather than doubling the consumed network resources for few users. Figure 4 summarizes the main characteristics of this use case: +--------+----------------------------------------------------------+ | Pros | Limitations | +--------+----------------------------------------------------------+ | Simple | * CAPEX (e.g., bandwidth cost) | | | * Requires coordination between the content and the | | | network providers | | | * Despite DS-formatted content, extensions are still | | | required to deliver the content to IPv4-only receivers | | | when DS-Lite is deployed. | +--------+----------------------------------------------------------+ Figure 4: Main Characteristics. 3.4. Mono-Stack Multicast Delivery Infrastructure Consider now the case where the multicast content is reachable only with one single address family (i.e., IPv4 or IPv6). Depending on transition steps, the source could stay in IPv4 or move to IPv6. And the legacy receivers are IPv4-reachable while the new receivers may be IPv6-enabled. Jacquenet, et al. Expires September 8, 2011 [Page 9] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 +-------+------------+------------+------------+-------------+ | Use | Network | Source | Receiver | Use Case | | Cases |Capabilities| | | Categories | +-------+------------+------------+------------+-------------+ | 1 | | IPv4 | IPv6 | | +-------+ +------------+------------+ Translation | | 2 | IPv4 | IPv6 | IPv4 | | +-------+ +------------+------------+-------------+ | 3 | | IPv6 | IPv6 | Traversal | +-------+------------+------------+------------+-------------+ | 4 | | IPv4 | IPv6 | | +-------+ +------------+------------+ Translation | | 5 | IPv6 | IPv6 | IPv4 | | +-------+ +------------+------------+-------------+ | 6 | | IPv4 | IPv4 | Traversal | +-------+------------+------------+------------+-------------+ | | | IPv4, IPv6 | IPv4, IPv6 | | |Hybrid*| IPv4, IPv6 +------------+------------+ Hybrid | | | | IPv4, IPv6 | IPv4, IPv6 | | +-------+------------+------------+------------+-------------+ Figure 5: Mono-stack use cases * In Hybrid cases, the network is partially IPv4 and partially IPv6. See below: --------------- // R4 S4 \\ S6 = v6 Source / +----+ | R6 = v6 Receiver +----+ IPv4 | DR |----| S4 = v4 Source R6 ---| QR | Network +----+ |- S6 R4 = v4 Receiver +----+ / | DR = Designated Router \\ // QR = IGMP/MLD Querier --------------- Figure 6: IPv4 Delivery Network Jacquenet, et al. Expires September 8, 2011 [Page 10] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 --------------- // R6 S6 \\ S6 = v6 Source / +----+ | R6 = v6 Receiver +----+ IPv6 | DR |----| S4 = v4 Source R4 ---| QR | Network +----+ |- S4 R4 = v4 Receiver +----+ / | DR = Designated Router \\ // QR = IGMP/MLD Querier --------------- Figure 7: IPv6 Delivery Network --------------- -------------- // R6 S6 \\ // R4 S4 \\ / IPv6 +------+ IPv4 \ | Network | MR | Network | \ +------+ / \\ // \\ // -------------- --------------- S6 = v6 Source R6 = v6 Receiver S4 = v4 Source R4 = v4 Receiver MR = Multicast Router, could be border router connecting IPv4 and IPv6 network, or DR connecting the source, or QR connecting the receiver Figure 8: Hybrid Delivery Network 3.4.1. Translation Cases If the multicast source and receiver are belonging to different address families, translation happens. The locations of translation functions defers according to the address family of delivery network. The translation can happen either close to the source or close to the receiver. Depending on the deployment model, this decision may result a different transition technology being selected. Only a single distribution tree is required if only one address family is serviced by a given transport network. The content will be delivered once which is better utilized the network bandwidth. However if the application relies on the IP information stored in the payload (e.g., SDP), then translation will break the application. Jacquenet, et al. Expires September 8, 2011 [Page 11] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 +-----------------------+-------------------------------------------+ | Pros | Limitations | +-----------------------+-------------------------------------------+ | Bandwidth utilization | * Receivers have to know the translated | | | source address in the context SSM | | | * Receivers would have to know the | | | translated multicast group address | | | * The information loss during the | | | translation operations | | | * The burden and necessary coordinations | | | are involved if stateful translations are | | | employed | | | * ALGs may be required to assist the | | | discovery of source address and multicast | | | group address | +-------------------------------------------------------------------+ Figure 9: Main Characteristics of translation-based schemes. [NOTE: Access to IPv6-only multicast content by legacy customers is not seen as a valid scenario; especially in the context of IP TV service offering. Whenever this configuration is met by an operator, it MAY consider the following mitigation alternatives: * Enable IPv4-IPv6 interconnection functions to allow the successful delivery of IPv6-only multicast content to IPv4-only receivers * Or swap the receiver device (e.g., STB) with a new dual-stack one if the provider controls STB and/or CP router devices.] 3.4.2. Traversal Cases If the multicast source and receiver are belonging to the same address family, while the delivery network is not. A viable scenario for this use case is DS-Lite Model: Customers with legacy receivers must continue to access the IPv4-enabled multicast services. This means the traffic should be accessed over IPv4. The following cases should be covered by any candidate solution to the issue of forwarding IPv4 multicast traffic in DS-Lite environment: (1) IPv4-only multicast receiver; (2) Dual-Stack multicast receiver. As for the content, two scenarios are considered as valid ones: (1) IPv4-only content; (2) Dual-Stack content (i.e., content reachable in both IPv4 and IPv6). Note that: Jacquenet, et al. Expires September 8, 2011 [Page 12] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 1. The legacy IPv4 receiver can access dual-stack and IPv4-only content. No issue is induced by this scenario. Multicast flows will be delivered using native IPv4 transfer mode. 2. An IPv4-only receiver behind a DS-Lite CGN: Additional functions are required to deliver the content to the receiver; 3. A dual stack receiver should access a dual stack content using IPv6. No extra function is required to implement this scenario; 4. Dual-Stack receiver accessing IPv4-only content: This scenario is similar to the IPv4-only receiver accessing the IPv4-only content (2nd bullet). Additional functions are required. In order to deliver IPv4 multicast flows to DS-Lite serviced users, two solution flavors can be envisaged: +---------------+---------------------------------------------------+ | Solution | Characteristics | | Flavor | | +---------------+---------------------------------------------------+ | Translation | For IPv4 content, introduce an IPv4-IPv6 | | | translator in the provider's network. Multicast | | | streams will then be delivered to the receivers | | | using IPv6 until the CPE. A second level of NAT | | | can then be enforced if the receiver is | | | IPv4-only | | +---------------------------------------------------+ | | This solution may require two | | | translation levels, can impact the overall | | | performance of the CPE, may alter the perceived | | | quality of experience, etc. This solution may be | | | the source of service disruption (especially for | | | live TV broadcasting). This is not desirable | | +---------------------------------------------------+ | | For IPv6 content, all streams are delivered to | | | the DS-Lite CPE using IPv6; an IPv4-IPv6 | | | translator can be enabled in the CPE to forward | | | the streams to an IPv4-only receiver. The | | | IPv4-IPv6 translation function may impact the | | | performance of the CPE | +---------------+---------------------------------------------------+ | Encapsulation | To access IPv4 content from an IPv4-only or | | | dual-stack receiver: If the receiver encapsulates | | | the multicast signaling, it will result packet | | | replication per tunnel interface. If the | | | underneath network is not aware of the multicast | | | topology, it will deliver the encapsulated | Jacquenet, et al. Expires September 8, 2011 [Page 13] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 | | multicast packets as unicast packets. The | | | replication will happen at the encapsulator | | | rather than the edge multicast router. This | | | would poorly utilize the network bandwidth | | +---------------------------------------------------+ | | This problem could be mitigated. If the | | | encapsulator translates the multicast group | | | address to another address family and uses it for | | | the multicast signaling, the underneath network | | | could build a multicast distribution tree using | | | the translated multicast address. Thus, the | | | network could deliver the encapsulated packets in | | | the standard multicast fashion using the | | | multicast delivery tree built by the translated | | | multicast address group. In other words, the | | | encapsulator bridges two multicast trees at the | | | control plane but performs encapsulation at the | | | data plane. This is a hybrid of translation and | | | encapsulation mechanisms | | +---------------------------------------------------+ | | Since legacy IPv4-only receivers are predominant, | | | it is optimal to enable the IPv4-IPv6 | | | encapsulation function closer to the receivers | | | (e.g., first IP node). Doing so, would lead to a | | | single core multicast tree and flow replication | | | to DS-Lite serviced devices will occur upon | | | request. Multicast flows are not replicated in | | | the core and aggregation network | | +---------------------------------------------------+ | | If the IPv4-IPv6 encapsulation function is | | | implemented deeper in the network, and since | | | legacy customers need to be serviced in IPv4, | | | multicast flows are likely to be duplicated | | | (native, encapsulated) which is not optimal | | +---------------------------------------------------+ | | The IPv4-in-IPv6 encapsulated multicast flows | | | destined to IPv4-embedded IPv6 group address are | | | treated as any IPv6 multicast flows, and can be | | | replicated within Multicast VLANs. | | | Mechanisms such as MLD Snooping or MLD Proxying | | | can be introduced into the distributed | | | Access Network Nodes which could behave as MLD | | | Queriers and replicate multicast flows as | | | appropriate | | +---------------------------------------------------+ | | To access IPv6 content from a dual-stack | | | receiver: No new function is required since | | | native multicast IPv6 functions can be used | Jacquenet, et al. Expires September 8, 2011 [Page 14] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 +---------------+---------------------------------------------------+ 4. Issues and Required Functions It is not so easy to provide a single solution which will be convenient for all Service Providers. This is even complex if we consider real deployments where the network is a collection of: Legacy, DS, DS-Lite, PPP, DHCP, GE, ATM, PIM-SM, SSM, P2MP LSP, mVPN, etc. However, the following requirements should be taken into account. 4.1. Fast Zapping The IGMP Leave latency may be an issue when considering channel zapping. In current IPv4-based TV service offerings, when a user changes a TV channel, an IGMP Leave message is sent followed by an IGMP Report to join a new channel. This may lead to two channels to be sent to the receiver and as a consequence a traffic peak which may cause congestion on access links is experienced. A procedure called IGMP fast-leave is commonly used to avoid this problem and to immediately stop the multicast stream as soon as the IGMP Leave is received. In current deployments, IGMP fast-leave requires activation of the IGMP Proxy in DSLAM. Fast zapping issues MUST be taken into account when dealing with IPv4-IPv6 multicast delivery. 4.2. Group and Source Discovery Considerations An ALG is required to help an IPv6 receiver to select the appropriate IP address when only the IPv4 address is advertised (e.g., using SDP); otherwise the access to the IPv4 multicast content can not be offered to the IPv6 receiver. The ALG may be located downstream the receiver. As such, the ALG does not know in advance whether the receiver is dual-stack or IPv6- only. The ALG may be tuned to insert both the original IPv4 address and corresponding IPv6 multicast address using for instance the ALTC SDP attribute [I-D.boucadair-mmusic-altc]. In order to avoid involving an ALG in the path, an IPv4-only source can advertise both its IPv4 address and IPv4-embedded IPv6 multicast address using for instance the ALTC SDP attribute. However, a dual- stack receiver may prefer to use the IPv6 address to receive the Jacquenet, et al. Expires September 8, 2011 [Page 15] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 multicast content. This address selection would require multicast flows to cross an IPv4-IPv6 interconnection function. 4.3. Subscription Multicast distribution trees are receiver-initiated. IPv4 receivers that wish to subscribe to an IPv4 multicast group will send the corresponding IGMP Report message towards the relevant IGMP Querier. In case the underlying network is IPv6, the information conveyed in IGMP messages should be relayed into corresponding MLD messages. 4.4. Multicast Tree Computation Grafting to an IPv4 multicast distribution tree through an IPv6 multicast domain suggests that IPv4 multicast traffic will have to be conveyed along an "IPv6-equivalent" multicast distribution tree. That is, part of the multicast distribution tree along which IPv4 multicast traffic will be forwarded SHOULD be computed and maintained by means of the PIMv6 machinery, so that the distribution tree can be terminated as close to the IPv4 receivers as possible for the sake of the multicast forwarding efficiency. This assumes a close interaction between the PIM designs enforced in both domains. Such interaction may be further complicated by different combinations: the IPv4 multicast domain is SSM-enabled (with no RP routers), while the IPv6 multicast domain may support both ASM and SSM [RFC3569] modes. For instance, the ASM mode would be used to optimize the forwarding of IPv4 multicast data sent by different sources into the IPv6 multicast domain by selecting privileged RP routers that could be located at the border between the IPv6 and the IPv4 multicast domains. 4.5. SLA Considerations Some contract agreements may prevent a network provider to alter the content as sent by the content provider, in particular for copyright, confidentiality and SLA assurance reasons. The streams should be delivered without alteration to requesting users. Crossing a NAT or enforcing an encapsulation may lead to fragmentation or extra delays and therefore impact the perceived quality of service. 4.6. Load Balancing In some operational network, a source-based NAT function is used for load-balancing purposes. Because of some operational issues induced by this NAT function, plans to remove the stateful NAT function are Jacquenet, et al. Expires September 8, 2011 [Page 16] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 adopted by some operators. Since the same concern apply for stateful IPv4-IPv6 translation function, stateless interconnection function SHOULD be privileged. [To be further elaborated] 4.7. Bandwidth Consumption As a reminder, to optimize the usage of network resources, all multicast streams are conveyed in the core network while only popular ones are continuously conveyed in the aggregation/access network (static mode). Non-popular streams are conveyed in the access network upon request (dynamic mode). [To be further elaborated] 4.8. ASM-SSM Considerations PIM-SSM is currently used in IP TV service offerings. [To be further elaborated: ASM with unicast-based prefix can be used in the IPv6 realm while SSM is used in the IPv4 domain.] 4.9. Interconnection Functions As mentioned above, several interconnection functions are required. These functions can be divided into: 1. Interworking functions for control messages 2. Interconnection function for data flows. 4.9.1. Interworking Functions for Control Flows The following sub-sections describes some interworking functions which may be required. 4.9.1.1. IGMP-MLD Interworking IGMP-MLD Interworking Function combines the IGMP/MLD Proxying function specified in [RFC4605] and the IGMP/MLD adaptation function which is meant to reflect the contents of IGMP messages into MLD messages, vice versa. For example, when an IGMP Report message is received from a receiver to subscribe to a given multicast group G (and optionally associated to a source if SSM mode is used), the IGMP-MLD Interworking Function Jacquenet, et al. Expires September 8, 2011 [Page 17] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 MUST send an MLD Report message to subscribe to the corresponding IPv6 group. 4.9.1.2. IPv4-IPv6 PIM Interworking [RFC4601] allows the computation of PIM-based IPv4 or IPv6 distribution trees; PIM is IP version agnostic. There is no specific IPv6 PIM machinery that would work differently than an IPv4 PIM machinery. The new things needed for the IPv4-IPv6 PIM Interworking Function are just to allow the PIM message received from one address family to correspondingly trigger the operation of the other address family per PIM machinery specified. The address mapping MUST performed similarly to that of the IGMP-MLD Interworking Function. 4.9.1.3. MLD-IPv4 PIM Interworking This function is required when the MLD Querier is connected to an IPv4 PIM realm and not an IPv6 one. The address mapping MUST performed similarly to that of the IGMP-MLD Interworking Function. 4.9.1.4. IGMP-IPv6 PIM Interworking Similar to the previous sub-section. The address mapping MUST performed similarly to that of the IGMP-MLD Interworking Function. 4.9.1.5. PIMv6-IGMP or PIMv4-MLD Interworking [To be further elaborated] 4.9.2. Interconnection Function for Traffic Flows According to different scenarios, translation or encapsulation mechanism can be used for traffic flows interconnection. The behaviour of this interconnection function MUST be specified. 5. Conclusions The analysis above has shown: Jacquenet, et al. Expires September 8, 2011 [Page 18] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 1. Operational networks are complex environments; these networks are likely to be hybrid ones. 2. Some issues are deployment-specific (e.g., density of IPv6- enabled customers attached to an access network, if only few IPv6-enabled receivers are in use it is more convenient to convey multicast traffic over IPv4 rather than doubling the consumed network resources for few users, etc.); 3. For all use cases, a solution is required for the delivery of multicast-based services to DS-Lite serviced customers. 4. For DS-Lite, encapsulation and translation solutions rely on the same control functions; the only difference is in the treatement of data flows. 5. Standardizing the algorithms for IPv4-IPv6 Interworking functions should be undertaken for both encapsulation and translation. 6. Some performance analysis are required to assess the impact of activating some extra functions on the CP routers (e.g., assess the impact of de-capsulation fucntion compared to transalation function, evaluate the impact on CP router when several receiers are behind the same CP router, etc.). 6. IANA Considerations This document makes no request of IANA. Note to RFC Editor: this section may be removed on publication as an RFC. 7. Security Considerations Access to contents in a multicast-enabled environment raises different security issues that have been already documented. This draft does not introduce any specific security issue. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Jacquenet, et al. Expires September 8, 2011 [Page 19] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [RFC3569] Bhattacharyya, S., "An Overview of Source-Specific Multicast (SSM)", RFC 3569, July 2003. [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006. [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", RFC 4605, August 2006. 8.2. Informative References [I-D.boucadair-mmusic-altc] Boucadair, M., Kaplan, H., Gilman, R., and S. Veikkolainen, "Session Description Protocol (SDP) Alternate Connectivity (ALTC) Attribute", draft-boucadair-mmusic-altc-01 (work in progress), September 2010. [I-D.ietf-mboned-auto-multicast] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. Pusateri, "Automatic IP Multicast Without Explicit Tunnels (AMT)", draft-ietf-mboned-auto-multicast-10 (work in progress), March 2010. [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, November 1997. Authors' Addresses Christian Jacquenet France Telecom Email: christian.jacquenet@orange-ftgroup.com Jacquenet, et al. Expires September 8, 2011 [Page 20] Internet-Draft IPv4-IPv6 Multicast: Problem Statement March 2011 Mohamed Boucadair France Telecom Rennes 35000 France Email: mohamed.boucadair@orange-ftgroup.com Yiu Lee Comcast US Email: Yiu_Lee@Cable.Comcast.com Jacni Qin ZTE China Email: jacniq@gmail.com Tina Tsou Huawei Technologies (USA) 2330 Central Expressway Santa Clara, CA 95050 USA Phone: +1 408 330 4424 Email: tena@huawei.com Jacquenet, et al. Expires September 8, 2011 [Page 21]