UDP acknowledgements are not applicable (source really doesn't care if packet was received)
224.0.0.0 to 239.255.255.255 is set aside for multicast.
224.0.0.X range is reserved and NEVER FORWARDED outside the local subnet.
224.0.1.X is also a reserved range but does get forwarded.
Examples are 224.0.1.39 and 224.0.1.40 - used for Cisco AUTO RP Discovery.
239.0.0.0/8 range reserved for testing own multicast applications.