Broadcast and Multicast MAC Addresses

Often with WiFi networks it is necessary to transmit the same bit of information to all stations. To facilitate this, the WiFi specification includes a special broadcast address. Expressed as the MAC FF:FF:FF:FF:FF:FF, transmissions destined to this address are meant for all stations in the vicinity.

While normally a WiFi interface is only concerned with traffic to and from its own MAC address, the default behavior is to also listen for messages bound to the broadcast address. An example of which is a beacon – a frame which advertises the presence of an access point. A beacon sent to broadcast will be “seen” by all stations in the area.

Similarly, a multicast address is a special type of address which operates like a broadcast address for the most part. Multicast addresses are used to set groups of devices which must communicate to many devices simultaneously, or special services such as mDNS and other service discovery protocols.