3Com Switch 4500 Family Manual page 319

One port belongs to only one multicast VLAN.
The port connected to a user terminal must be a hybrid port.
The multicast member port must be in the same multicast VLAN with the router port. Otherwise, the
port cannot receive multicast packets.
If a router port is in a multicast VLAN, the router port must be configured as a trunk port or a hybrid
port that allows tagged packets to pass for the multicast VLAN. Otherwise, all the multicast
member ports in this multicast VLAN cannot receive multicast packets.
If a multicast member port needs to receive multicast packets forwarded by a router port that does
not belong to any multicast VLAN, the multicast member port must be removed from the multicast
VLAN. Otherwise, the port cannot receive multicast packets.
Examples
# Configure VLAN 2 as a multicast VLAN.
<Sysname> system-view
System View: return to User View with Ctrl+Z.
[Sysname] vlan 2
[Sysname-vlan2] service-type multicast
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