3-13 Multicast VLAN ConfigurationWhen configuring multicast VLAN, go to these sections for information you are interested in:z Introduction to Multicast VLANz Multicast VLAN Configuration Task Listz Configuring Sub-VLAN-Based Multicast VLANz Configuring Port-Based Multicast VLANz Displaying and Maintaining Multicast VLANz Multicast VLAN Configuration ExamplesIntroduction to Multicast VLANAs shown in Figure 3-1, in the traditional multicast programs-on-demand mode, when hosts, Host A,Host B and Host C, belonging to different VLANs require multicast programs on demand service, theLayer 3 device, Router A, needs to forward a separate copy of the multicast traffic in each user VLANto the Layer 2 device, Switch A. This results in not only waste of network bandwidth but also extraburden on the Layer 3 device.Figure 3-1 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 needs to replicate the multicast traffic only in the multicastVLAN instead of making a separate copy of the multicast traffic in each user VLAN. This saves thenetwork bandwidth and lessens the burden of the Layer 3 device.The multicast VLAN feature can be implemented in two approaches, as described below:Sub-VLAN-based multicast VLANAs shown in Figure 3-2, Host A, Host B and Host C are in three different user VLANs. On Switch A,configure VLAN 10 as a multicast VLAN, configure all the user VLANs as sub-VLANs of this multicastVLAN, and enable IGMP Snooping in the multicast VLAN.
