Unicast, multicast, and broadcast are address types. A unicast address represents a single interface. A multicast address represents a group of interfaces. A broadcast address represents all interfaces of the local network.
Each frame contains two MAC addresses: a source address and a destination address. The source address belongs to the device that creates it. The destination address belongs to the device that receives it.
There are three types of MAC addresses. The following table lists them.
| Unicast | Represents a single device on the local network |
| Broadcast | Represents every device on the local network |
| Multicast | Represents a group of devices on the local network |
Since the creator of a frame can be only one device, the source address field of a frame always contains a unicast address. However, the recipients of the frame can be a single device, a group of devices, or all devices of the local network. Because of this, the destination address field of a frame can contain any address from the above-listed table.
A unicast address represents only one interface on the Ethernet LAN. A frame having a unicast address in the destination field is processed by only one network device on the segment.
The following image shows an example of a unicast.
In this example, PC-A creates an ethernet frame for PC-B and places it on the wire. All PCs examine the destination address of the frame. Since the frame contains the PC-B's address, PC-B processes the frame. All other PCs ignore the frame.
A multicast address represents a group of devices. A frame having a multicast address in the destination field is processed by multiple network devices on the segment.
The following image shows an example of a multicast.
In this example, PC-A creates an ethernet frame for PC-B and PC-C. Since the frame is intended for more than one PC and only one address can be used in the destination address field, PC-A uses an address that belongs to both PC-B and PC-C. In simple words, it uses the group address of both PCs. Technically, this address is known as a multicast address.
All PCs examine the destination address of the frame. Since the frame contains the group address of PC-B and PC-C, both process the frame. All other PCs ignore the frame.
A broadcast address represents all devices of the network. A frame having a broadcast address in the destination field is processed by all network devices on the segment.
The following image shows an example of a broadcast.
In this example, PC-A creates an ethernet frame for all devices on the local segment. Since the frame is intended for all devices, PC-A uses an address that belongs to all devices.
All PCs examine the destination address of the frame. Since the frame contains the broadcast address and the broadcast address belongs to all devices, all devices process the frame.
