65Configuring multicast VLANsOverviewIn the traditional multicast programs-on-demand mode shown in Figure 21, when hosts (Host A, Host Band Host C) that belong to different VLANs require multicast programs-on-demand service, the Layer 3device, Router A, must forward a separate copy of the multicast traffic in each user VLAN to the Layer 2device, Switch A. This results in not only waste of network bandwidth but also extra burden on the Layer3 device.Figure 21 Multicast transmission without multicast VLANThe multicast VLAN feature configured on the Layer 2 device is the solution to this issue. With themulticast VLAN feature, the Layer 3 device replicates the multicast traffic only in the multicast VLANinstead of making a separate copy of the multicast traffic in each user VLAN. This saves networkbandwidth and lessens the burden on the Layer 3 device.The multicast VLAN feature can be implemented in sub-VLAN-based multicast VLAN and port-basedmulticast VLAN.Sub-VLAN-based multicast VLANAs shown in Figure 22, Host A, Host B, and Host C are in different user VLANs. On Switch A, configureVLAN 10 as a multicast VLAN, configure all the user VLANs as sub-VLANs of VLAN 10, and enableIGMP snooping in the multicast VLAN.SourceReceiverHost AMulticast packets VLAN 2VLAN 3VLAN 4VLAN 2VLAN 3VLAN 4Switch AReceiverHost BReceiverHost CRouter AIGMP querier
