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Forward transmission and reverse transmission
The device supports both forward transmission and reverse transmission for multicast VLAN.
In forward transmission, multicast receivers are connected to downstream devices of a Layer 2
device. The Layer 2 device forwards multicast traffic only from the upstream Layer 3 device to
downstream devices that are in sub-VLANs or have member ports.
In reverse transmission, multicast sources are connected to downstream devices of a Layer 2
device. Upon receiving multicast traffic from a downstream multicast source, the Layer 2 device
changes the user VLAN of the traffic to the associated multicast VLAN. Then, it floods the traffic to
the upstream Layer 3 device through the multicast VLAN. The upstream Layer 3 device forwards the
traffic to receivers based on the associated Layer 3 multicast forwarding entry.
Multicast VLAN configuration task list
Tasks at a glance
(Required.) Perform one of the following tasks:
Configuring a sub-VLAN-based multicast VLAN
•
Configuring a port-based multicast VLAN
Configuring user port attributes
Assigning user ports to a multicast VLAN
Setting the maximum number of multicast VLAN forwarding entries
When you configure the multicast VLANs, follow these guidelines:
•
If you have configured both a sub-VLAN-based multicast VLAN and a port-based multicast
VLAN on a device, the port-based multicast VLAN configuration takes effect.
•
The multicast VLAN feature does not take effect on secondary VLANs. As a best practice, do
not configure the multicast VLAN feature for secondary VLANs. For more information about
secondary VLANs, see
Layer 2
—
LAN Switching Configuration Guide
.
Configuring a sub-VLAN-based multicast VLAN
To configure a sub-VLAN-based multicast VLAN, configure a VLAN as a multicast VLAN, and assign
the VLANs that contain multicast receivers to the multicast VLAN as sub-VLANs.
Configuration prerequisites
Before you configure a sub-VLAN-based multicast VLAN, complete the following tasks:
•
Create VLANs as required.
•
Enable IGMP snooping for the VLAN to be configured as the multicast VLAN, and for the
VLANs to be configured as sub-VLANs.
Configuration restrictions and guidelines
When you configure a sub-VLAN-based multicast VLAN, follow these restrictions and guidelines:
•
The VLAN to be configured as the multicast VLAN must exist.
•
The VLANs to be configured as sub-VLANs of the multicast VLAN must exist and cannot be
multicast VLANs or sub-VLANs of any other multicast VLAN.
•
The total number of multicast VLANs on a device cannot exceed the upper limit.