Multicast Listener Discovery (MLD) for IPv6
RFC 2710
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RFC - Proposed Standard
(October 1999; No errata)
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2013-03-02
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RFC 2710 (Proposed Standard)
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Network Working Group S. Deering
Request for Comments: 2710 Cisco Systems
Category: Standards Track W. Fenner
AT&T Research
B. Haberman
IBM
October 1999
Multicast Listener Discovery (MLD) for IPv6
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 Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document specifies the protocol used by an IPv6 router to
discover the presence of multicast listeners (that is, nodes wishing
to receive multicast packets) on its directly attached links, and to
discover specifically which multicast addresses are of interest to
those neighboring nodes. This protocol is referred to as Multicast
Listener Discovery or MLD. MLD is derived from version 2 of IPv4's
Internet Group Management Protocol, IGMPv2. One important difference
to note is that MLD uses ICMPv6 (IP Protocol 58) message types,
rather than IGMP (IP Protocol 2) message types.
1. Definitions
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 [KEYWORDS].
2. Introduction
The purpose of Multicast Listener Discovery (MLD) is to enable each
IPv6 router to discover the presence of multicast listeners (that is,
nodes wishing to receive multicast packets) on its directly attached
links, and to discover specifically which multicast addresses are of
interest to those neighboring nodes. This information is then
Deering, et al. Standards Track [Page 1]
RFC 2710 Multicast Listener Discovery for IPv6 October 1999
provided to whichever multicast routing protocol is being used by the
router, in order to ensure that multicast packets are delivered to
all links where there are interested receivers.
MLD is an asymmetric protocol, specifying different behaviors for
multicast listeners and for routers. For those multicast addresses
to which a router itself is listening, the router performs both parts
of the protocol, including responding to its own messages.
If a router has more than one interface to the same link, it need
perform the router part of MLD over only one of those interfaces.
Listeners, on the other hand, must perform the listener part of MLD
on all interfaces from which an application or upper-layer protocol
has requested reception of multicast packets.
3. Message Format
MLD is a sub-protocol of ICMPv6, that is, MLD message types are a
subset of the set of ICMPv6 messages, and MLD messages are identified
in IPv6 packets by a preceding Next Header value of 58. All MLD
messages described in this document are sent with a link-local IPv6
Source Address, an IPv6 Hop Limit of 1, and an IPv6 Router Alert
option [RTR-ALERT] in a Hop-by-Hop Options header. (The Router Alert
option is necessary to cause routers to examine MLD messages sent to
multicast addresses in which the routers themselves have no
interest.)
MLD messages have the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Response Delay | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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+ +
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+ Multicast Address +
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+ +
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