1. Introduction

The Multicast Listener Discovery (MLD) protocol [RFC2710] is used by an IPv6 router to discover the presence of multicast listeners on its directly attached links, and to discover specifically which multicast addresses are of interest to those neighboring nodes. MLD is derived from Version 2 of the Internet Group Management Protocol (IGMPv2) [RFC2236] for IPv4. IGMPv2 allows IPv4 nodes to report interest in receiving packets sent to a particular multicast group address. IGMPv3 [RFC3376] adds the ability for IPv4 nodes to report interest in receiving packets sent to a particular multicast group address ONLY from specific source addresses, or from ALL source addresses EXCEPT for specific source addresses. This information may be used by multicast routing protocols to avoid delivering multicast packets from specific sources to networks where there are no interested listeners.

This document specifies Version 2 of MLD, which is derived from IGMPv3. MLDv2 is backward compatible with MLDv1, and is specified to interoperate correctly with nodes that implement MLDv1. This document describes the behavior of MLDv2 nodes; the behavior of MLDv1 nodes is specified in [RFC2710].

MLDv2 protocol packets are sent using authenticated link-local IPv6 communication. However, this specification does not define the security mechanisms to be used. Instead, it relies on the IPsec Authentication Header (AH) [RFC2402] or Encapsulating Security Payload (ESP) [RFC2406] to provide authentication of MLDv2 messages. The specific security requirements for MLDv2 are described in the Security Considerations section of this document.