3Com 4510G Configuration Manual page 422

Figure 3-2 Sub-VLAN-based multicast VLAN
Multicast packets
VLAN 10 (Multicast VLAN)
VLAN 2
VLAN 3
VLAN 4
Source Router A
IGMP querier
After the configuration, IGMP Snooping manages router ports in the multicast VLAN and member ports
in the sub-VLANs. When forwarding multicast data to Switch A, Router A needs to send only one copy
of multicast traffic to Switch A in the multicast VLAN, and Switch A distributes the traffic to the multicast
VLAN's sub-VLANs that contain receivers.
Port-based multicast VLAN
As shown in Figure 3-3, Host A, Host B and Host C are in three different user VLANs. All the user ports
(ports with attached hosts) on Switch A are hybrid ports. On Switch A, configure VLAN 10 as a
multicast VLAN, assign all the user ports to this multicast VLAN, and enable IGMP Snooping in the
multicast VLAN and all the user VLANs.
Figure 3-3 Port-based multicast VLAN
After the configuration, upon receiving an IGMP message on a user port, Switch A tags the message
with the multicast VLAN ID and relays it to the IGMP querier, so that IGMP Snooping can uniformly
manage the router ports and member ports in the multicast VLAN. When forwarding multicast data to
Switch A, Router A needs to send only one copy of multicast traffic to Switch A in the multicast VLAN,
and Switch A distributes the traffic to all the member ports in the multicast VLAN.
Switch A
3-2
VLAN 2
Receiver
Host A
VLAN 3
Receiver
Host B
VLAN 4
Receiver
Host C