© Copyright Lenovo 2016 Chapter 33: Multicast Listener Discovery 525How MLD WorksThe software uses the information obtained through MLD to maintain a list ofmulticast group memberships for each interface and forwards the multicast trafficonly to interested listeners.Without MLD, the switch forwards IPv6 multicast traffic through all ports,increasing network load. Following is an overview of operations when MLD isconfigured on the G8264: The switch acts as an Mrouter when MLDv1/v2 is configured and enabled oneach of its directly attached links. If the switch has multiple interfaces connectedto the same link, it operates the protocol on any one of the interfaces. If there are multiple Mrouters on the subnet, the Mrouter with the numericallylowest IPv6 address is elected as the Querier. The Querier sends general queries at short intervals to learn multicast addresslistener information from an attached link. Hosts respond to these queries by reporting their per‐interface MulticastAddress Listening state, through Current State Report messages sent to aspecific multicast address that all MLD routers on the link listen to. If the listening state of a host changes, the host immediately reports thesechanges through a State Change Report message. The Querier sends a Multicast Address Specific Query to verify if hosts arelistening to a specified multicast address or not. Similarly, if MLDv2 isconfigured, the Querier sends a Multicast Address and Source Specific Query toverify, for a specified multicast address, if hosts are listening to a specific set ofsources, or not. MLDv2 listener report messages consists of Multicast AddressRecords: INCLUDE: to receive packets from source specified in the MLDv2 message EXCLUDE: to receive packets from all sources except the ones specified in theMLDv2 message A host can send a State Change Report to indicate its desire to stop listening to aparticular multicast address (or source in MLDv2). The Querier then sends amulticast address specific query to verify if there are other listeners of themulticast address. If there aren’t any, the Mrouter deletes the multicast addressfrom its Multicast Address Listener state and stops sending multicast traffic.Similarly in MLDv2, the Mrouter sends a Multicast Address and Source SpecificQuery to verify if, for a specified multicast address, there are hosts still listeningto a specific set of sources.G8264 supports MLD versions 1 and 2.Note: MLDv2 operates in version 1 compatibility mode when, in a specificnetwork, not all hosts are configured with MLDv2.
