Using Internet Group Management Protocol Version 3 (IGMPv3) and Multicast Listener Discovery Protocol Version 2 (MLDv2) for Source-Specific Multicast
Network Working Group H. Holbrook
Request for Comments: 4604 Arastra, Inc.
Updates: 3376, 3810 B. Cain
Category: Standards Track Acopia Networks
Using Internet Group Management Protocol Version 3 (IGMPv3)
and Multicast Listener Discovery Protocol Version 2 (MLDv2)
for Source-Specific Multicast
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2006).
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.
Holbrook, et al. Standards Track [Page 1]
RFC 4604 IGMPv3/MLDv2 for SSM August 2006
The Internet Group Management Protocol (IGMP) [RFC1112, IGMPv2,
IGMPv3] allows an IPv4 host to communicate IP multicast group
membership information to its neighboring routers. IGMP version 3
(IGMPv3) [IGMPv3] provides the ability for a host to selectively
request or filter traffic from individual sources within a multicast
The Multicast Listener Discovery Protocol (MLD) [RFC2710, MLDv2]
offers similar functionality for IPv6 hosts. MLD version 2 (MLDv2)
provides the analogous "source filtering" functionality of IGMPv3 for
Due to the commonality of function, the term "Group Management
Protocol", or "GMP", will be used to refer to both IGMP and MLD. The
term "Source Filtering GMP", or "SFGMP", will be used to refer
jointly to the IGMPv3 and MLDv2 group management protocols.
The use of source-specific multicast is facilitated by small changes
to the SFGMP protocols on both hosts and routers. [SSM] defines
general requirements that must be followed by systems that implement
the SSM service model; this document defines the concrete application
of those requirements to systems that implement IGMPv3 and MLDv2. In
doing so, this document defines modifications to the host and router
portions of IGMPv3 and MLDv2 for use with SSM, and presents a number
of clarifications to their behavior when used with SSM addresses.
This document updates the IGMPv3 and MLDv2 specifications.
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].
In order to emphasize the parts of this document that modify the
existing protocol specifications ([RFC2710, MLDv2, IGMPv3]), as
opposed to merely clarify them, any protocol modifications are marked
with the tag "MODIFICATION".
2. Host Requirements for Source-Specific Multicast
This section defines the notion of an "SSM-aware" host and then goes
on to describe the API requirements and the SFGMP protocol
requirements of an SSM-aware host. It is important to note that SSM
can be used by any host that supports source filtering APIs and whose
operating system supports the appropriate SFGMP. The SFGMP
Holbrook, et al. Standards Track [Page 2]
RFC 4604 IGMPv3/MLDv2 for SSM August 2006
modifications described in this section make SSM work better on an
SSM-aware host, but they are not strict prerequisites for the use of
The 232/8 IPv4 address range is currently allocated for SSM by IANA
[IANA-ALLOCATION]. In IPv6, the FF3x::/32 range (where 'x' is a
valid IPv6 multicast scope value) is reserved for SSM semantics
[RFC3306], although today SSM allocations are restricted to
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