H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 344)

30-1
30
Multicast VLAN Configuration
Introduction to Multicast VLAN
As shown in Figure 30-1 , in the traditional multicast programs-on-demand mode, when hosts that
belong to different VLANs, Host A, Host B and Host C require multicast programs on demand service,
Router A needs to forward a separate copy of the multicast data in each VLAN. This results in not only
waste of network bandwidth but also extra burden on the Layer 3 device.
Figure 30-1 Before and after multicast VLAN is enabled on the Layer 2 device
Multicast packet transmission
without Multicast VLAN
Source
Router A
Multicast packets
Multicast packet transmission
when Multicast VLAN runs
Source
Router A
Switch A
Host A
Receiver
Host B
Receiver
Host C
Receiver
VLAN 30
VLAN 20
VLAN 10
Switch A
Host A
Receiver
Host B
Receiver
Host C
Receiver
VLAN 30
VLAN 20
VLAN 10
To solve this problem, you can enable the multicast VLAN feature on Switch A, namely configure the
VLANs to which these hosts belong as sub-VLANs of a multicast VLAN on the Layer 2 device and
enable Layer 2 multicast in the multicast VLAN. After this configuration, Router A replicates the
multicast data only within the multicast VLAN instead of forwarding a separate copy of the multicast
data to each VLAN. This saves the network bandwidth and lessens the burden of the Layer 3 device.
Configuring Multicast VLAN
Follow these steps to configure a multicast VLAN:
To do… Use the command… Remarks
Enter system view system-view —
Configure a specific VLAN as a
multicast VLAN
multicast -vlan vlan-id enable
Required
Disabled by default