An Overview of Source-Specific Multicast (SSM)
RFC 3569
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RFC - Informational
(July 2003; No errata)
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Author |
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Supratik Bhattacharya
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Last updated |
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2015-10-14
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IETF
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(None)
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No shepherd assigned
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IESG |
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RFC 3569 (Informational)
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Unknown
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Alex Zinin
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Network Working Group S. Bhattacharyya, Ed.
Request for Comments: 3569 Sprint
Category: Informational July 2003
An Overview of Source-Specific Multicast (SSM)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The purpose of this document is to provide an overview of
Source-Specific Multicast (SSM) and issues related to its deployment.
It discusses how the SSM service model addresses the challenges faced
in inter-domain multicast deployment, changes needed to routing
protocols and applications to deploy SSM and interoperability issues
with current multicast service models.
1. Introduction
This document provides an overview of the Source-Specific Multicast
(SSM) service and its deployment using the PIM-SM and IGMP/MLD
protocols. The network layer service provided by SSM is a "channel",
identified by an SSM destination IP address (G) and a source IP
address S. An IPv4 address range has been reserved by IANA for use
by the SSM service. An SSM destination address range already exists
for IPv6. A source S transmits IP datagrams to an SSM destination
address G. A receiver can receive these datagrams by subscribing to
the channel (Source, Group) or (S,G). Channel subscription is
supported by version 3 of the IGMP protocol for IPv4 and version2 of
the MLD protocol for IPv6. The interdomain tree for forwarding IP
multicast datagrams is rooted at the source S, and is constructed
using the PIM Sparse Mode [9] protocol.
This document is not intended to be a standard for Source-Specific
Multicast (SSM). Instead, its goal is to serve as an introduction to
SSM and its benefits for anyone interested in deploying SSM services.
It provides an overview of SSM and how it solves a number of problems
faced in the deployment of inter-domain multicast. It outlines
changes to protocols and applications both at end-hosts and routers
Bhattacharyya Informational [Page 1]
RFC 3569 An Overview of SSM July 2003
for supporting SSM, with pointers to more detailed documents where
appropriate. Issues of interoperability with the multicast service
model defined by RFC 1112 are also discussed.
This memo is a product of the Source-Specific Multicast (SSM) Working
Group of the Internet Engineering Task Force.
The keywords "MUST"", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as defined in BCP 14, RFC 2119 [28].
2. Terminology
This section defines some terms that are used in the rest of this
document:
Any-Source Multicast (ASM): This is the IP multicast service model
defined in RFC 1112 [25]. An IP datagram is transmitted to a
"host group", a set of zero or more end-hosts (or routers)
identified by a single IP destination address (224.0.0.0 through
239.255.255.255 for IPv4). End-hosts may join and leave the group
any time, and there is no restriction on their location or number.
Moreover, this model supports multicast groups with arbitrarily
many senders - any end-host (or router) may transmit to a host
group, even if it is not a member of that group.
Source-Specific Multicast (SSM): This is the multicast service
model defined in [5]. An IP datagram is transmitted by a source S
to an SSM destination address G, and receivers can receive this
datagram by subscribing to channel (S,G). SSM provides host
applications with a "channel" abstraction, in which each channel
has exactly one source and any number of receivers. SSM is
derived from earlier work in EXPRESS [1]. The address range 232/8
has been assigned by IANA for SSM service in IPv4. For IPv6, the
range FF3x::/96 is defined for SSM services [21].
Source-Filtered Multicast (SFM): This is a variant of the ASM
service model, and uses the same address range as ASM
(224.0.0.0-239.255.255.255). It extends the ASM service model as
follows. Each "upper layer protocol module" can now request data
sent to a host group G by only a specific set of sources, or can
request data sent to host group G from all BUT a specific set of
sources. Support for source filtering is provided by version 3 of
the Internet Group Management Protocol (or IGMPv3) [3] for IPv4,
and version 2 of the Multicast Listener Discovery (or MLDv2) [22]
protocol for IPv6. We shall henceforth refer to these two
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