Types of Ethernet Addresses
Ethernet addresses, also frequently called MAC addresses, are 6 bytes in length, typically listed in
hexadecimal form. There are three main types of Ethernet address, as listed in Table 1-4.
Most engineers instinctively know how unicast and broadcast addresses are used in a typical
network. When an Ethernet NIC needs to send a frame, it puts its own unicast address in the Source
Address field of the header. If it wants to send the frame to a particular device on the LAN, the
sender puts the other device’s MAC address in the Ethernet header’s Destination Address field.
If the sender wants to send the frame to every device on the LAN, it sends the frame to the
FFFF.FFFF.FFFF broadcast destination address. (A frame sent to the broadcast address is named
a broadcast or broadcast frame, and frames sent to unicast MAC addresses are called unicasts or
unicast frames.)
Multicast Ethernet frames are used to communicate with a possibly dynamic subset of the devices
on a LAN. The most common use for Ethernet multicast addresses involves the use of IP multicast.
For example, if only 3 of 100 users on a LAN want to watch the same video stream using an IP
multicast–based video application, the application can send a single multicast frame. The three
interested devices prepare by listening for frames sent to a particular multicast Ethernet address,
Three Types of Ethernet/MAC Address
Type of Ethernet/MAC
Address Description and Notes
Unicast Fancy term for an address that represents a single LAN interface. The
I/G bit, the most significant bit in the most significant byte, is set to 0.
Broadcast An address that means “all devices that reside on this LAN right
now.” Always a value of hex FFFFFFFFFFFF.
Multicast A MAC address that implies some subset of all devices currently on
the LAN. By definition, the I/G bit is set to 1.