IPv6 Multicast Protocols

Table 1 describes multicast protocols on an IPv6 network.

**Table 1** IPv6 multicast protocols
Protocol	Function	Remarks
Multicast Listener Discovery (MLD)	MLD manages IPv6 multicast group members and runs on the end of a multicast network (network segments where Layer 3 multicast devices connect to user hosts). Hosts use the MLD protocol to join or leave multicast groups. Layer 3 multicast devices use the MLD protocol to manage and maintain group memberships. MLD can interact with upper-layer multicast routing protocols.	MLD has two versions: MLDv1 and MLDv2. MLDv2 can be independently used in the source-specific multicast (SSM) model, whereas MLDv1 must use SSM mapping. MLD works on an IPv6 network in the same way IGMP works on an IPv4 network. MLDv1 is similar to IGMPv2, and MLDv2 is similar to IGMPv3.
Protocol Independent Multicast (PIM) for IPv6	IPv6 PIM runs on an IPv6 network and sends multicast data to multicast devices connected to multicast group members interested in the data. IPv6 PIM works in sparse mode (PIM-SM) or dense mode (PIM-DM). IPv6 PIM-SM applies to large-scale networks with sparsely distributed group members, and IPv6 PIM-DM applies to small-scale networks with densely distributed group members.	IPv6 PIM-DM does not need to differentiate between the any-source multicast (ASM) and SSM models. IPv6 PIM-SM differentiates between the ASM and SSM models based on multicast addresses in multicast data and protocol packets. If multicast addresses of packets are in the SSM group address range, IPv6 PIM-SM uses the SSM model to provide multicast services. The IPv6 PIM-SSM model is efficient and simplifies the multicast address allocation process. It is applicable when a group has only one specific source. If multicast addresses of packets are in the ASM group address range, IPv6 PIM-SM uses the ASM model to provide multicast services.
MLD snooping & MLD snooping Proxy	On an IPv6 network, MLD snooping enables a switch to create and maintain a Layer 2 multicast forwarding table by listening to MLD packets exchanged between the upstream Layer 3 device and user hosts. The switch controls forwarding of multicast data packets based on the Layer 2 multicast forwarding table to reduce multicast data flooding on the Layer 2 network. MLD snooping proxy enables the switch to act in place of the upstream Layer 3 device to send Query messages to downstream hosts, and in place of downstream hosts to send MLD Report/Done messages to the upstream Layer 3 device. This function saves bandwidth between the upstream device and local switch.	MLD snooping works on an IPv6 network in the same way IGMP snooping works on an IPv4 network.