Operation Manual – MulticastH3C S7500E Series Ethernet Switches Chapter 3 Multicast VLAN Configuration3-1Chapter 3 Multicast VLAN Configuration3.1 Introduction to Multicast VLANAs shown in Figure 3-1, in the traditional multicast programs-on-demand mode, whenhosts that belong to different VLANs, Host A, Host B and Host C require multicastprograms on demand service, Router A needs to forward a separate copy of themulticast data in each VLAN. This results in not only waste of network bandwidth butalso extra burden on the Layer 3 device.Multicast packet transmissionwithout Multicast VLANSourceRouter AMulticast packetsMulticast packet transmissionwhen Multicast VLAN runsSourceRouter ASwitch AHost AReceiverHost BReceiverHost CReceiverVLAN 30VLAN 20VLAN 10Switch AHost AReceiverHost BReceiverHost CReceiverVLAN 30VLAN 20VLAN 10Figure 3-1 Before and after multicast VLAN is enabled on the Layer 2 deviceTo solve this problem, you can enable the multicast VLAN feature on Switch A, namelyconfigure the VLANs to which these hosts belong as sub-VLANs of a multicast VLANon the Layer 2 device and enable Layer 2 multicast in the multicast VLAN. After thisconfiguration, Router A replicates the multicast data only within the multicast VLANinstead of forwarding a separate copy of the multicast data to each VLAN. This savesthe network bandwidth and lessens the burden of the Layer 3 device.3.2 Configuring Multicast VLANFollow these steps to configure a multicast VLAN:
