O'Reilly logo
  • Manouchehr Jalayer thinks this is interesting:

This causes a 32-to-1 IP multicast address-to-multicast MAC address ambiguity (25 = 32).


Cover of IP Multicast, Volume 1: Cisco IP Multicast Networking


23 bits of Multicast class D is used to identify the Mac Address of the multicast group.

Because the high order 4 bits of class D address is '1110' for all multicast groups, we will have 5 bits of the layer 3 address with no effect on identifying the Mac address.

5 bits represent 32 numbers, so 32 multicast group gets a single Mac address.

1 Mac -> 32 Multicast address