Unicast: individual device to receive the frame
Multicast: group of devices to receive the frame, like radio, one transmit and group receive
Broadcast: all devices in the current network segment, always = FFFFFFFFFFFF
I/G = Individual group, 0 means unicast, 1 means multicast.
U/G = Universal group, 0 means the address in vendor assigned, 1 means the address is administratively assigned, overriding the vendor-assigned address.
So, the first byte of the MAC address is either 00, 01, 02, 03:
00 = unicast, vendor assigned
01 = multicast, vendor assigned
02 = unicast, administratively assigned
03 = multicast, administratively assigned
By setting the MAC address administratively (by hand), the device driver would not enforce the U/G to be 1, so we are able to set the MAC address to some freaky address of our choice, yet when it is being dynamically set, the U/G will be set to 1 automatically.
Here is the Switch behavior whenever a frame hits an interface incoming:
Type of Address
Forwards frame out the single interface associated with the destination address
Floods frame out all interfaces, except the interface on which the frame was received
Floods frame identically to unknown unicasts
Floods frame identically to unknown unicasts, unless multicast optimizations are conﬁgured