As described, IGMP/MLD snooping only forwards incoming Join or Leave messages via router ports. In a structure with multiple bridges, initially none of the ports are router ports or members of a multicast group. If a station connected to the bridge registers with a multicast group, the port automatically becomes a member of this group. However, none of the ports are router ports at this phase, so the Join messages are not forwarded anywhere. Other bridges thus receive no information about the port's membership with the multicast group.