Multicast Listener Discovery (MLD) for IPv6
RFC 2710

• Status
• IESG evaluation record
• IESG writeups
• Email expansions
• History

• Versions
• 02

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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Multicast Address                       +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Deering, et al.             Standards Track                     [Page 2]
RFC 2710         Multicast Listener Discovery for IPv6      October 1999