There are three types of Ethernet addresses:
1. Unicast Addresses
Unicast addresses represent a single LAN interface. A unicast frame will be sent to a specific device, not to a group of devices on the LAN:
The unicast address will have the value of the MAC address of the destination device.
2. Multicast Addresses
Multicast addresses represent a group of devices in a LAN. A frame sent to a multicast address will be forwarded to a group of devices on the LAN:
Multicast frames have a value of 1 in the least-significant bit of the first octet of the destination address. This helps a network switch to distinguish between unicast and multicast addresses. One example of an Ethernet multicast address would be 01:00:0C:CC:CC:CC, which is the address used by CDP (Cisco Discovery Protocol).
3. Broadcast Addresses
Broadcast addresses represent all devices on the LAN. Frames sent to a broadcast address will be delivered to all devices on the LAN:
The broadcast address has the value of FFFF.FFFF.FFFF (all binary ones). The switch will flood broadcast frames out of all ports except the port that it was received on.
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