Deprecating Any-Source Multicast (ASM) for Interdomain Multicast

Stockholm Sweden swmike@swm.pp.se

Jisc

Lumen House, Library Avenue Harwell Oxford Didcot OX11 0SG United Kingdom tim.chown@jisc.ac.uk

Juniper Networks, Inc.

2251 Corporate Park Drive Herndon Virginia 20171 United States of America lenny@juniper.net

Futurewei Technologies Inc.

2330 Central Expy Santa Clara California 95050 United States of America tte@cs.fau.de

Operations Mboned This document recommends deprecation of the use of Any-Source Multicast (ASM) for interdomain multicast. It recommends the use of Source-Specific Multicast (SSM) for interdomain multicast applications and recommends that hosts and routers in these deployments fully support SSM. The recommendations in this document do not preclude the continued use of ASM within a single organization or domain and are especially easy to adopt in existing deployments of intradomain ASM using PIM Sparse Mode (PIM-SM).

Status of This Memo This memo documents an Internet Best Current Practice. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents () 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

. Introduction
. Background
- . Multicast Service Models
- . ASM Routing Protocols
  - . PIM Sparse Mode (PIM-SM)
  - . Embedded-RP
  - . BIDIR-RP
- . SSM Routing Protocols
. Discussion
- . Observations on ASM and SSM Deployments
- . Advantages of SSM for Interdomain Multicast
  - . Reduced Network Operations Complexity
  - . No Network-Wide IP Multicast Group-Address Management
  - . Intrinsic Source-Control Security
. Recommendations
- . Deprecating Use of ASM for Interdomain Multicast
- . Including Network Support for IGMPv3/MLDv2
- . Building Application Support for SSM
- . Developing Application Guidance: SSM, ASM, Service Discovery
- . Preferring SSM Applications Intradomain
- . Documenting an ASM/SSM Protocol Mapping Mechanism
- . Not Filtering ASM Addressing between Domains
- . Not Precluding Intradomain ASM
- . Evolving PIM Deployments for SSM
. Future Interdomain ASM Work
. Security Considerations
. IANA Considerations
. References
- . Normative References
- . Informative References
Acknowledgments
Authors' Addresses

Introduction IP Multicast has been deployed in various forms, within private networks, the wider Internet, and federated networks such as national or regional research networks. While a number of service models have been published, and in many cases revised over time, there has been no strong recommendation made by the IETF on the appropriateness of those models to certain scenarios, even though vendors and federations have often made such recommendations. This document addresses this gap by making a BCP-level recommendation to deprecate the use of Any-Source Multicast (ASM) for interdomain multicast, leaving Source-Specific Multicast (SSM) as the recommended interdomain mode of multicast. Therefore, this document recommends that all hosts and routers that support interdomain multicast applications fully support SSM. This document does not make any statement on the use of ASM within a single domain or organization and, therefore, does not preclude its use. Indeed, there are application contexts for which ASM is currently still widely considered well suited within a single domain. The main issue in most cases with moving to SSM is application support. Many applications are initially deployed for intradomain use and are later deployed interdomain. Therefore, this document recommends that applications support SSM, even when they are initially intended for intradomain use. As explained below, SSM applications are readily compatible with existing intradomain ASM deployments using PIM-SM, as PIM-SSM is merely a subset of PIM-SM.

Background

Multicast Service Models Any-Source Multicast (ASM) and Source-Specific Multicast (SSM) are the two multicast service models in use today. In ASM, as originally described in , receivers express interest in joining a multicast group address, and routers use multicast routing protocols to deliver traffic from the sender(s) to the receivers. If there are multiple senders for a given group, traffic from all senders will be delivered to the receivers. Since receivers specify only the group address, the network -- and therefore the multicast routing protocols -- are responsible for source discovery. In SSM, by contrast, receivers specify both group and source when expressing interest in joining a multicast stream. Source discovery in SSM is handled by some out-of-band mechanism (typically in the application layer), which drastically simplifies the network and how the multicast routing protocols operate. IANA has reserved specific ranges of IPv4 and IPv6 address space for multicast addressing. Guidelines for IPv4 multicast address assignments can be found in , while guidelines for IPv6 multicast address assignments can be found in and . The IPv6 multicast address format is described in .

ASM Routing Protocols

PIM Sparse Mode (PIM-SM) The most commonly deployed ASM routing protocol is Protocol Independent Multicast - Sparse Mode (PIM-SM), as detailed in . PIM-SM, as the name suggests, was designed to be used in scenarios where the subnets with receivers are sparsely distributed throughout the network. Because receivers do not indicate sender addresses in ASM (but only group addresses), PIM-SM uses the concept of a Rendezvous Point (RP) as a "meeting point" for sources and receivers, and all routers in a PIM-SM domain are configured to use a specific RP(s), either explicitly or through dynamic RP-discovery protocols. To enable PIM-SM to work between multiple domains, an interdomain, inter-RP signaling protocol known as Multicast Source Discovery Protocol (MSDP) is used to allow an RP in one domain to learn of the existence of a source in another domain. Deployment scenarios for MSDP are given in . MSDP floods information about all active sources for all multicast streams to all RPs in all the domains -- even if there is no receiver for a given application in a domain. As a result of this key scalability and security issue, along with other deployment challenges with the protocol, MSDP was never extended to support IPv6 and remains an Experimental protocol. At the time of writing, there is no IETF interdomain solution at the level of Proposed Standard for IPv4 ASM multicast, because MSDP was the de facto mechanism for the interdomain source discovery problem, and it is Experimental. Other protocol options were investigated at the same time but were never implemented or deployed and are now historic (e.g., ).

Embedded-RP Due to the availability of more bits in an IPv6 address than in IPv4, an IPv6-specific mechanism was designed in support of interdomain ASM, with PIM-SM leveraging those bits. Embedded-RP allows routers supporting the protocol to determine the RP for the group without any prior configuration or discovery protocols, simply by observing the unicast RP address that is embedded (included) in the IPv6 multicast group address. Embedded-RP allows PIM-SM operation across any IPv6 network in which there is an end-to-end path of routers supporting this mechanism, including interdomain deployment.

BIDIR-RP BIDIR-PIM is another protocol to support ASM. There is no standardized option to operate BIDIR-PIM interdomain. It is deployed intradomain for applications where many sources send traffic to the same IP multicast groups because, unlike PIM-SM, it does not create per-source state. BIDIR-PIM is one of the important reasons for this document to not deprecate intradomain ASM.

SSM Routing Protocols SSM is detailed in . It mandates the use of PIM-SSM for routing of SSM. PIM-SSM is merely a subset of PIM-SM . PIM-SSM expects the sender's source address(es) to be known in advance by receivers through some out-of-band mechanism (typically in the application layer); thus, the receiver's designated router can send a PIM Join message directly towards the source without needing to use an RP. IPv4 addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as Source-Specific Multicast (SSM) destination addresses and are reserved for use by source-specific applications and protocols. For IPv6, the address prefix ff3x::/32 is reserved for source-specific multicast use. See .

Discussion

Observations on ASM and SSM Deployments In enterprise and campus scenarios, ASM in the form of PIM-SM is likely the most commonly deployed multicast protocol. The configuration and management of an RP (including RP redundancy) within a single domain is a well-understood operational practice. However, if interworking with external PIM domains is needed in IPv4 multicast deployments, interdomain MSDP is required to exchange information about sources between domain RPs. Deployment experience has shown MSDP to be a complex and fragile protocol to manage and troubleshoot. Some of these issues include complex Reverse Path Forwarding (RPF) rules, state attack protection, and filtering of undesired sources. PIM-SM is a general-purpose protocol that can handle all use cases. In particular, it was designed for cases such as videoconferencing where multiple sources may come and go during a multicast session. But for cases where a single, persistent source for a group is used, and receivers can be configured to know of that source, PIM-SM has unnecessary complexity. Therefore, SSM removes the need for many of the most complex components of PIM-SM. As explained above, MSDP was not extended to support IPv6. Instead, the proposed interdomain ASM solution for PIM-SM with IPv6 is Embedded-RP, which allows the RP address for a multicast group to be embedded in the group address, making RP discovery automatic for all routers on the path between a receiver and a sender. Embedded-RP can support lightweight ad hoc deployments. However, it relies on a single RP for an entire group that could only be made resilient within one domain. While this approach solves the MSDP issues, it does not solve the problem of unauthorized sources sending traffic to ASM multicast groups; this security issue is one of biggest problems of interdomain multicast. As stated in RFC 4607, SSM is particularly well suited to either dissemination-style applications with one or more senders whose identities are known (by some out-of-band mechanism) before the application starts running or applications that utilize some signaling to indicate the source address of the multicast stream (e.g., an electronic programming guide in IPTV applications). Therefore, SSM through PIM-SSM is very well suited to applications such as classic linear-broadcast TV over IP. SSM requires applications, host operating systems, and the designated routers connected to receiving hosts to support Internet Group Management Protocol, Version 3 (IGMPv3) and Multicast Listener Discovery, Version 2 (MLDv2) . While support for IGMPv3 and MLDv2 has been commonplace in routing platforms for a long time, it has also now become widespread in common operating systems for several years (Windows, Mac OS, Linux/Android) and is no longer an impediment to SSM deployment.

Advantages of SSM for Interdomain Multicast This section describes the three key benefits that SSM with PIM-SSM has over ASM. These benefits also apply to intradomain deployment but are even more important in interdomain deployments. See for more details.

Reduced Network Operations Complexity A significant benefit of SSM is the reduced complexity that comes through eliminating the network-based source discovery required in ASM with PIM-SM. Specifically, SSM eliminates the need for RPs, shared trees, Shortest Path Tree (SPT) switchovers, PIM registers, MSDP, dynamic RP-discovery mechanisms (Bootstrap Router (BSR) / AutoRP), and data-driven state creation. SSM simply utilizes a small subset of PIM-SM, alongside the integration with IGMPv3/MLDv2, where the source address signaled from the receiver is immediately used to create (S,G) state. Eliminating network-based source discovery for interdomain multicast means the vast majority of the complexity of multicast goes away. This reduced complexity makes SSM radically simpler to manage, troubleshoot, and operate, particularly for backbone network operators. This is the main operator motivation for the recommendation to deprecate the use of ASM in interdomain scenarios. Note that this discussion does not apply to BIDIR-PIM, and there is (as mentioned above) no standardized interdomain solution for BIDIR-PIM. In BIDIR-PIM, traffic is forwarded to the RP instead of building state as in PIM-SM. This occurs even in the absence of receivers. Therefore, BIDIR-PIM offers a trade-off of state complexity at the cost of creating unnecessary traffic (potentially a large amount).

No Network-Wide IP Multicast Group-Address Management In ASM, IP multicast group addresses need to be assigned to applications and instances thereof, so that two simultaneously active application instances will not share the same group address and receive IP multicast traffic from each other. In SSM, no such IP multicast group management is necessary. Instead, the IP multicast group address simply needs to be assigned locally on a source like a unicast transport protocol port number: the only coordination required is to ensure that different applications running on the same host don't send to the same group address. This does not require any network-operator involvement.

Intrinsic Source-Control Security SSM is implicitly secure against off-path unauthorized/undesired sources. Receivers only receive packets from the sources they explicitly specify in their IGMPv3/MLDv2 membership messages, as opposed to ASM, where any host can send traffic to a group address and have it transmitted to all receivers. With PIM-SSM, traffic from sources not requested by any receiver will be discarded by the First-Hop Router (FHR) of that source, minimizing source attacks against shared network bandwidth and receivers. This benefit is particularly important in interdomain deployments because there are no standardized solutions for ASM control of sources and the most common intradomain operational practices such as Access Control Lists (ACLs) on the sender's FHR are not feasible for interdomain deployments. This topic is expanded upon in .

Recommendations This section provides recommendations for a variety of stakeholders in SSM deployment, including vendors, operators, and application developers. It also suggests further work that could be undertaken within the IETF.

Deprecating Use of ASM for Interdomain Multicast This document recommends that the use of ASM be deprecated for interdomain multicast; thus, implicitly, it recommends that hosts and routers that support such interdomain applications fully support SSM and its associated protocols. Best current practices for deploying interdomain multicast using SSM are documented in . The recommendation applies to the use of ASM between domains where either MSDP (IPv4) or Embedded-RP (IPv6) is used. An interdomain use of ASM multicast in the context of this document is one where PIM-SM with RPs/MSDP/Embedded-RP is run on routers operated by two or more separate administrative entities. The focus of this document is deprecation of interdomain ASM multicast, and while encouraging the use of SSM within domains, it leaves operators free to choose to use ASM within their own domains. A more inclusive interpretation of this recommendation is that it also extends to deprecating use of ASM in the case where PIM is operated in a single operator domain, but where user hosts or non-PIM network edge devices are under different operator control. A typical example of this case is a service provider offering IPTV (single operator domain for PIM) to subscribers operating an IGMP proxy home gateway and IGMPv3/MLDv2 hosts (computer, tablets, set-top boxes).

Including Network Support for IGMPv3/MLDv2 This document recommends that all hosts, router platforms, and security appliances used for deploying multicast support the components of IGMPv3 and MLDv2 necessary to support SSM (i.e., explicitly sending source-specific reports). "IPv6 Node Requirements" states that MLDv2 must be supported in all implementations. Such support is already widespread in common host and router platforms. Further guidance on IGMPv3 and MLDv2 is given in . Multicast snooping is often used to limit the flooding of multicast traffic in a Layer 2 network. With snooping, an L2 switch will monitor IGMP/MLD messages and only forward multicast traffic out on host ports that have interested receivers connected. Such snooping capability should therefore support IGMPv3 and MLDv2. There is further discussion in .

Building Application Support for SSM The recommendation to use SSM for interdomain multicast means that applications should properly trigger the sending of IGMPv3/MLDv2 source-specific report messages. It should be noted, however, that there is a wide range of applications today that only support ASM. In many cases, this is due to application developers being unaware of the operational concerns of networks and the implications of using ASM versus SSM. This document serves to provide clear direction for application developers who might currently only consider using ASM to instead support SSM, which only requires relatively minor changes for many applications, particularly those with single sources. It is often thought that ASM is required for multicast applications where there are multiple sources. However, RFC 4607 also describes how SSM can be used instead of PIM-SM for multi-party applications:

SSM can be used to build multi-source applications where all participants' identities are not known in advance, but the multi-source "rendezvous" functionality does not occur in the network layer in this case. Just like in an application that uses unicast as the underlying transport, this functionality can be implemented by the application or by an application-layer library.

Some useful considerations for multicast applications can be found in .

Developing Application Guidance: SSM, ASM, Service Discovery Applications with many-to-many communication patterns can create more (S,G) state than is feasible for networks to manage, whether the source discovery is done by ASM with PIM-SM or at the application level and SSM/PIM-SSM. These applications are not best supported by either SSM/PIM-SSM or ASM/PIM-SM. Instead, these applications are better served by routing protocols that do not create (S,G), such as BIDIR-PIM. Unfortunately, many applications today use ASM solely for service discovery. One example is where clients send IP multicast packets to elicit unicast replies from server(s). Deploying any form of IP multicast solely in support of such service discovery is, in general, not recommended. Dedicated service discovery via DNS-based Service Discovery (DNS-SD) should be used for this instead. This document describes best practices to explain when to use SSM in applications -- e.g., when ASM without (S,G) state in the network is better, or when dedicated service-discovery mechanisms should be used. However, specifying how applications can support these practices is outside the scope of this document. Further work on this subject may be expected within the IETF.

Preferring SSM Applications Intradomain If feasible, it is recommended for applications to use SSM even if they are initially only meant to be used in intradomain environments supporting ASM. Because PIM-SSM is a subset of PIM-SM, existing intradomain PIM-SM networks are automatically compatible with SSM applications. Thus, SSM applications can operate alongside existing ASM applications. SSM's benefits of simplified address management and significantly reduced operational complexity apply equally to intradomain use. However, for some applications, it may be prohibitively difficult to add support for source discovery, so intradomain ASM may still be appropriate.

Documenting an ASM/SSM Protocol Mapping Mechanism In the case of existing ASM applications that cannot readily be ported to SSM, it may be possible to use some form of protocol mapping -- i.e., to have a mechanism to translate a (*,G) join or leave to a (S,G) join or leave for a specific source S. The general challenge in performing such mapping is determining where the configured source address, S, comes from. There are existing vendor-specific mechanisms deployed that achieve this function, but none are documented in IETF documents. This may be a useful area for the IETF to work on as an interim transition mechanism. However, these mechanisms would introduce additional administrative burdens, along with the need for some form of address management, neither of which are required in SSM. Hence, this should not be considered a long-term solution.

Not Filtering ASM Addressing between Domains A key benefit of SSM is that the receiver specifies the source-group tuple when signaling interest in a multicast stream. Hence, the group address need not be globally unique, so there is no need for multicast address allocation as long the reserved SSM range is used. Despite the deprecation of interdomain ASM, it is recommended that operators not filter ASM group ranges at domain boundaries, as some form of ASM-SSM mappings may continue to be used for some time.

Not Precluding Intradomain ASM The use of ASM within a single multicast domain such as a campus or enterprise is still relatively common today. There are even global enterprise networks that have successfully been using PIM-SM for many years. The operators of such networks most often use Anycast-RP or MSDP (with IPv4) for RP resilience, at the expense of the extra operational complexity. These existing practices are unaffected by this document. In the past decade, some BIDIR-PIM deployments have scaled interdomain ASM deployments beyond the capabilities of PIM-SM. This, too, is unaffected by this document; instead, it is encouraged where necessary due to application requirements (see ). This document also does not preclude continued use of ASM with multiple PIM-SM domains inside organizations, such as with IPv4 MSDP or IPv6 Embedded-RP. This includes organizations that are federations and have appropriate, nonstandardized mechanisms to deal with the interdomain ASM issues explained in .

Evolving PIM Deployments for SSM Existing PIM-SM deployments can usually be used to run SSM applications with few-to-no changes. In some widely available router implementations of PIM-SM, PIM-SSM is simply enabled by default in the designated SSM address spaces whenever PIM-SM is enabled. In other implementations, simple configuration options exist to enable it. This allows migration of ASM applications to SSM/PIM-SSM solely through application-side development to handle source-signaling via IGMPv3/MLDv2 and using SSM addresses. No network actions are required for this transition; unchanged ASM applications can continue to coexist without issues. When running PIM-SM, IGMPv3/MLDv2 (S,G) membership reports may also result in the desired PIM-SSM (S,G) operations and bypass any RP procedures. This is not standardized but depends on implementation and may require additional configuration in available products. In general, it is recommended to always use SSM address space for SSM applications. For example, the interaction of IGMPv3/MLDv2 (S,G) membership reports and BIDIR-PIM is undefined and may not result in forwarding of any traffic. Note that these migration recommendations do not include considerations on when or how to evolve those intradomain applications best served by ASM/BIDIR-PIM from PIM-SM to BIDIR-PIM. This may also be important but is outside the scope of this document.

Future Interdomain ASM Work Future work may attempt to overcome current limitations of ASM solutions, such as interdomain deployment solutions for BIDIR-PIM or source-access-control mechanisms for IPv6 PIM-SM with embedded-RP. Such work could modify or amend the recommendations of this document (like any future IETF Standards Track / BCP work). Nevertheless, it is very unlikely that any ASM solution, even with such future work, can ever provide the same intrinsic security and network- and address-management simplicity as SSM (see ). Accordingly, this document recommends that future work for general-purpose interdomain IP multicast focus on SSM items listed in .

Security Considerations This document adds no new security considerations. It instead removes security issues incurred by interdomain ASM with PIM-SM/MSDP, such as infrastructure control-plane attacks and application and bandwidth/congestion attacks from unauthorized sources sending to ASM multicast groups. RFC 4609 describes the additional security benefits of using SSM instead of ASM.

IANA Considerations This document has no IANA actions.

References Normative References Host extensions for IP multicasting This memo specifies the extensions required of a host implementation of the Internet Protocol (IP) to support multicasting. Recommended procedure for IP multicasting in the Internet. This RFC obsoletes RFCs 998 and 1054. [STANDARDS-TRACK] Allocation Guidelines for IPv6 Multicast Addresses Internet Group Management Protocol, Version 3 Multicast Listener Discovery Version 2 (MLDv2) for IPv6 This document updates RFC 2710, and it specifies Version 2 of the ulticast Listener Discovery Protocol (MLDv2). MLD is used by an IPv6 router to discover the presence of multicast listeners on directly attached links, and to discover which multicast addresses are of interest to those neighboring nodes. MLDv2 is designed to be interoperable with MLDv1. MLDv2 adds the ability for a node to report interest in listening to packets with a particular multicast address only from specific source addresses or from all sources except for specific source addresses. [STANDARDS-TRACK] Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address This memo defines an address allocation policy in which the address of the Rendezvous Point (RP) is encoded in an IPv6 multicast group address. For Protocol Independent Multicast - Sparse Mode (PIM-SM), this can be seen as a specification of a group-to-RP mapping mechanism. This allows an easy deployment of scalable inter-domain multicast and simplifies the intra-domain multicast configuration as well. This memo updates the addressing format presented in RFC 3306. [STANDARDS-TRACK] IP Version 6 Addressing Architecture This specification defines the addressing architecture of the IP Version 6 (IPv6) protocol. The document includes the IPv6 addressing model, text representations of IPv6 addresses, definition of IPv6 unicast addresses, anycast addresses, and multicast addresses, and an IPv6 node's required addresses. This document obsoletes RFC 3513, "IP Version 6 Addressing Architecture". [STANDARDS-TRACK] Source-Specific Multicast for IP IP version 4 (IPv4) addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast (SSM) destination addresses and are reserved for use by source-specific applications and protocols. For IP version 6 (IPv6), the address prefix FF3x::/32 is reserved for source-specific multicast use. This document defines an extension to the Internet network service that applies to datagrams sent to SSM addresses and defines the host and router requirements to support this extension. [STANDARDS-TRACK] IANA Guidelines for IPv4 Multicast Address Assignments This document provides guidance for the Internet Assigned Numbers Authority (IANA) in assigning IPv4 multicast addresses. It obsoletes RFC 3171 and RFC 3138 and updates RFC 2780. This memo documents an Internet Best Current Practice. Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised) This document specifies Protocol Independent Multicast - Sparse Mode (PIM-SM). PIM-SM is a multicast routing protocol that can use the underlying unicast routing information base or a separate multicast-capable routing information base. It builds unidirectional shared trees rooted at a Rendezvous Point (RP) per group, and it optionally creates shortest-path trees per source. This document obsoletes RFC 4601 by replacing it, addresses the errata filed against it, removes the optional (*,*,RP), PIM Multicast Border Router features and authentication using IPsec that lack sufficient deployment experience (see Appendix A), and moves the PIM specification to Internet Standard. Use of Multicast across Inter-domain Peering Points This document examines the use of Source-Specific Multicast (SSM) across inter-domain peering points for a specified set of deployment scenarios. The objectives are to (1) describe the setup process for multicast-based delivery across administrative domains for these scenarios and (2) document supporting functionality to enable this process. Informative References IPv6 Multicast Address Assignments This document defines the initial assignment of IPv6 multicast addresses. This memo provides information for the Internet community. It does not specify an Internet standard of any kind. IP Multicast Applications: Challenges and Solutions This document describes the challenges involved with designing and implementing multicast applications. It is an introductory guide for application developers that highlights the unique considerations of multicast applications as compared to unicast applications. This memo provides information for the Internet community. Multicast Source Discovery Protocol (MSDP) The Multicast Source Discovery Protocol (MSDP) describes a mechanism to connect multiple IP Version 4 Protocol Independent Multicast Sparse-Mode (PIM-SM) domains together. Each PIM-SM domain uses its own independent Rendezvous Point (RP) and does not have to depend on RPs in other domains. This document reflects existing MSDP implementations. Border Gateway Multicast Protocol (BGMP): Protocol Specification This document describes the Border Gateway Multicast Protocol (BGMP), a protocol for inter-domain multicast routing. BGMP builds shared trees for active multicast groups, and optionally allows receiver domains to build source-specific, inter-domain, distribution branches where needed. BGMP natively supports "source-specific multicast" (SSM). To also support "any-source multicast" (ASM), BGMP requires that each multicast group be associated with a single root (in BGMP it is referred to as the root domain). It requires that different ranges of the multicast address space are associated (e.g., with Unicast-Prefix-Based Multicast addressing) with different domains. Each of these domains then becomes the root of the shared domain-trees for all groups in its range. Multicast participants will generally receive better multicast service if the session initiator's address allocator selects addresses from its own domain's part of the space, thereby causing the root domain to be local to at least one of the session participants. This memo provides information for the Internet community. Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches This memo describes the recommendations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) snooping switches. These are based on best current practices for IGMPv2, with further considerations for IGMPv3- and MLDv2-snooping. Additional areas of relevance, such as link layer topology changes and Ethernet-specific encapsulation issues, are also considered. This memo provides information for the Internet community. Using Internet Group Management Protocol Version 3 (IGMPv3) and Multicast Listener Discovery Protocol Version 2 (MLDv2) for Source-Specific Multicast The Internet Group Management Protocol Version 3 (IGMPv3) and the Multicast Listener Discovery Protocol Version 2 (MLDv2) are protocols that allow a host to inform its neighboring routers of its desire to receive IPv4 and IPv6 multicast transmissions, respectively. Source-specific multicast (SSM) is a form of multicast in which a receiver is required to specify both the network-layer address of the source and the multicast destination address in order to receive the multicast transmission. This document defines the notion of an "SSM-aware" router and host, and clarifies and (in some cases) modifies the behavior of IGMPv3 and MLDv2 on SSM-aware routers and hosts to accommodate source-specific multicast. This document updates the IGMPv3 and MLDv2 specifications. [STANDARDS-TRACK] Protocol Independent Multicast - Sparse Mode (PIM-SM) Multicast Routing Security Issues and Enhancements This memo describes security threats for the larger (intra-domain or inter-domain) multicast routing infrastructures. Only Protocol Independent Multicast - Sparse Mode (PIM-SM) is analyzed, in its three main operational modes: the traditional Any-Source Multicast (ASM) model, the source-specific multicast (SSM) model, and the ASM model enhanced by the Embedded Rendezvous Point (Embedded-RP) group-to-RP mapping mechanism. This memo also describes enhancements to the protocol operations that mitigate the identified threats. This memo provides information for the Internet community. Anycast-RP Using Protocol Independent Multicast (PIM) This specification allows Anycast-RP (Rendezvous Point) to be used inside a domain that runs Protocol Independent Multicast (PIM) only. Other multicast protocols (such as Multicast Source Discovery Protocol (MSDP), which has been used traditionally to solve this problem) are not required to support Anycast-RP. [STANDARDS-TRACK] Multicast Source Discovery Protocol (MSDP) Deployment Scenarios This document describes best current practices for intra-domain and inter-domain deployment of the Multicast Source Discovery Protocol (MSDP) in conjunction with Protocol Independent Multicast Sparse Mode (PIM-SM). This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Bidirectional Protocol Independent Multicast (BIDIR-PIM) This document discusses Bidirectional PIM (BIDIR-PIM), a variant of PIM Sparse-Mode that builds bidirectional shared trees connecting multicast sources and receivers. Bidirectional trees are built using a fail-safe Designated Forwarder (DF) election mechanism operating on each link of a multicast topology. With the assistance of the DF, multicast data is natively forwarded from sources to the Rendezvous-Point (RP) and hence along the shared tree to receivers without requiring source-specific state. The DF election takes place at RP discovery time and provides the route to the RP, thus eliminating the requirement for data-driven protocol events. [STANDARDS-TRACK] DNS-Based Service Discovery This document specifies how DNS resource records are named and structured to facilitate service discovery. Given a type of service that a client is looking for, and a domain in which the client is looking for that service, this mechanism allows clients to discover a list of named instances of that desired service, using standard DNS queries. This mechanism is referred to as DNS-based Service Discovery, or DNS-SD. IPv6 Node Requirements This document defines requirements for IPv6 nodes. It is expected that IPv6 will be deployed in a wide range of devices and situations. Specifying the requirements for IPv6 nodes allows IPv6 to function well and interoperate in a large number of situations and deployments. This document obsoletes RFC 6434, and in turn RFC 4294.

Acknowledgments The authors would like to thank members of the IETF MBONE Deployment Working Group for discussions on the content of this document, with specific thanks to the following people for their contributions to the document: , , , , , , , , , , and .