From: mark_cruzNOTFORSPAM@hotmail.com   
      
   Hello   
      
   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?   
      
   Thanks.   
      
   --   
   Mark   
      
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