Multicast Listener Discovery (MLD) v1 and v2 snooping is a multicast-constraining mechanism that runs on Layer 2 or Layer 3 devices to manage and control IPv6 multicast groups.
A Layer 2 switch forwards all multicast control packets and data received on all member ports of a VLAN interface. This approach, though simple, is not bandwidth efficient, because only a subset of member ports may be connected to devices that are interested in receiving those multicast packets.
In the worst-case scenario, data is forwarded to all port members of a VLAN, even if only one VLAN member is interested in receiving the data. Such scenarios can lead to loss of throughput for a switch when it receives high-rate multicast data traffic.
MLD snooping is a multicast constraining mechanism that runs on Layer 2 or Layer 3 devices to manage and control IPv6 multicast groups. MLD snooping sends IPv6 multicast traffic only to interested listeners. By listening to and analyzing MLD messages, a Layer 2 device running MLD snooping establishes mappings between ports and multicast MAC addresses or multicast IP addresses, and forwards multicast data accordingly. Multicast routers in a network are found by means of static configuration, dynamic learning, or PIM hello-based mrouter detection.
| Scalability feature | Maximum |
|---|---|
| MLD group | 4000 |
| Number of snooping-enabled VLANS or bridge domains | 256 |
| Report learning rate | 512 frames per second |