Multicast Listener Discovery | 60527Multicast Listener DiscoveryMulticast Listener Discovery is supported only on platform: eMLD Snooping is supported only on platform: eMulticast Listener Discovery (MLD) is a Layer 3 protocol that IPv6 routers use to learn of the multicastreceivers that are directly connected to them and the groups in which the receivers are interested. Multicastrouting protocols (like PIM) use the information learned from MLD to route multicast traffic to allinterested receivers. MLD is analogous to IGMP, which tracks IPv4 multicast receivers.Protocol OverviewMLD version 1 is analogous to IGMP version 2. MLD version 3 adds the ability to include and excludesources and is analogous to IGMP version 3.MLD Version 1Routers use MLD to learn which multicast addresses have listeners on each of their attached links. Foreach link, the router keeps a list of which multicast addresses have listeners and a timer associated witheach of those addresses.There are three types of MLD messages:• Multicast Listener Query — a message sent by the Queerer to learn which multicast groups havelisteners.• General Query — a query to which all listeners should respond.• Multicast-Address-Specific Query — a query to which only listeners for the specified groupshould respond.• Multicast Listener Report — a message sent by listeners declaring their multicast groupsubscriptions.• Multicast Listener Done — a message sent by a listener declaring that it is leaving a multicast group.Figure 27-1 shows the packet structure of MLD version 1 packets.
