There are several deployment scenarios for delivering multicast directly over subscriber hosts:
1:1 model (subscriber per VLAN/SAP) with the Access Node (AN) that is not IGMP/MLD aware.
N:1 model (service per VLAN/SAP) with the AN in the Snooping mode.
N:1 model with the AN in the Proxy mode.
N:1 model with the AN that is not IGMP/MLD aware.
There are two modes of operation for subscriber multicast that can be chosen to address the above mentioned deployment scenarios:
Per SAP replication — A single multicast stream per group is forwarded on any given SAP. Even if the SAP has a multicast group (channel) that is registered to multiple hosts, only a single copy of the multicast stream is forwarded over this SAP. The multicast stream has a multicast destination MAC address (as opposed to unicast). IGMP/MLD states are maintained per host. This is the default mode of operation.
Per subscriber host replication in this mode of operation, multicast is replicated per subscriber host even if this means that multiple copies of the same stream that are forwarded over the same SAP. For example, if two hosts on the same SAP are registered to receive the same multicast group (channel), then this multicast channel is replicated twice on the same SAP. The streams have a unique unicast destination MAC address (otherwise it would not make sense to replicate the streams twice).
In all deployment scenarios and modes of operation the IGMP/MLD states per source IP address of the incoming IGMP/MLD message is maintained. This source IP address might represent a subscriber hosts or the AN (proxy mode).
For MLD, the source IP address is the host link local address. Therefore, the MLD message is associated with all IP address/prefix of the host.