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Configuring multicast VLANs
Overview
As shown in Figure 17, Host A, Host B, and Host C reside in different VLANs and join the same multicast
group. When Switch A (Layer 3 device) receives multicast data for that group, it sends three copies of the
multicast data to Switch B (Layer 2 device). This occupies large bandwidth and increases the burden on
the Layer 3 device.
Figure 17 Multicast transmission without the multicast VLAN feature
After a multicast VLAN is configured on Switch B, Switch A sends only one copy of the multicast data to
the multicast VLAN on Switch B. This method saves network bandwidth and lessens the burden on the
Layer 3 device.
Multicast VLANs include sub-VLAN-based multicast VLANs and port-based multicast VLANs.
Sub-VLAN-based multicast VLAN
As shown in Figure 18 :
• Host A, Host B, and Host C are in VLAN 2 through VLAN 4, respectively.
• On Switch B, VLAN 10 is a multicast VLAN. VLAN 2 through VLAN 4 are sub-VLANs of VLAN 10.
• IGMP snooping is enabled for the multicast VLAN and its sub-VLANs.
Source
Receiver
Host A
Multicast packets
VLAN 2
VLAN 3
VLAN 4
VLAN 2
VLAN 3
VLAN 4
Switch B
Receiver
Host B
Receiver
Host C
Switch A
IGMP querier
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