Unicast, multicast, and broadcast addresses

There are three types of Ethernet 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.
  • 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.
  • broadcast addresses – represent all device 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 all ports except the port that it was received on.
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 an address used by CDP (Cisco Discovery Protocol).



 

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