studying multicasting and IGMP specifically, and have a few points I don't clearly understand. First of all why do we need Ethernet multicast addresses, wouldn't IP multicasting suffice to distribure traffic among the groups of hosts? I only guess, there are protocols exploiting Ethernet-based multicasting?
And the second. From RFC1112: "IP host address is mapped to Ethernet multicast address by placing the low-order 23-bits of the IP address into the low-order 23 bits of Ethernet multicast address 01-00-5e-00-00-00".
Does this mean that in order to send a multicast packet, a host must supply a properly built MAC address in the form defined above, in its Ethernet header field (destination address)? So the OUI, purchased by equipment manufacturers would not suffice?