56
Figure 20 Sub-VLAN-based multicast VLAN
Source
Router A
IGMP querier
VLAN 2
VLAN 3
VLAN 4
Switch A
Receiver
Host A
Receiver
Host B
Receiver
Host C
Multicast packets
VLAN 2
VLAN 3
VLAN 4
VLAN 10 (Multicast VLAN)
After the configuration, IGMP snooping manages router ports in the multicast VLAN and member ports in
the sub-VLANs. When forwarding multicast data to Switch A, Router A sends only one copy of multicast
data to Switch A in the multicast VLAN, and Switch A distributes the data to the multicast VLAN’s sub-
VLANs that contain receivers.
Port-based multicast VLAN
As shown in Figure 21, Host A, Host B, and Host C are in different user VLANs. All user ports—ports
with attached hosts—on Switch A are hybrid ports. On Switch A, configure VLAN 10 as a multicast
VLAN, assign all user ports to VLAN 10, and enable IGMP snooping in the multicast VLAN and all user
VLANs.
Figure 21 Port-based multicast VLAN
After the configuration, upon receiving an IGMP message on a user port, Switch A tags the message
with the multicast VLAN ID and relays it to the IGMP querier, so that IGMP snooping can uniformly
manage the router port and member ports in the multicast VLAN. When Router A forwards multicast
data to Switch A, it sends only one copy of multicast data to Switch A in the multicast VLAN, and Switch
A distributes the data to all member ports in the multicast VLAN.
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