When the least significant bit of a MAC address’s first byte is 0, it
means the frame is meant to reach only one receiving NIC, which
means unicast traffic.
When the least significant bit of the first octet of a MAC address is 1, it
means the frame is a multicast frame, and the receiving NICs will
process it if they were configured to accept multicast MAC addresses.
An example of a multicast MAC address that is used by Cisco Discovery
Protocol (CDP) is 01-00-0C-CC-CC-CC.
When all the bits are set to 1, it means the frame is a broadcast frame,
and it is being received by all the NICs on that network segment.Each client that needs to exchange data on an Ethernet
network needs to have a unique MAC address so that the
data is directed to the proper destination device. The
MAC address is burned into the network interface card
(NIC) and is also called the burned-in address (BIA) or
the physical address of the device. A MAC address has 48
bits organized as 12 hexadecimal numbers. There are
several different ways of representing MAC addresses, all
of them containing the same information. The following
representations of a MAC address are all equivalent:
0000.0c59.beef
00:00:0c:59:be:ef
00-00-0C-59-BE-EFA MAC address has two components (see Figure 16-6):
Organizationally unique identifier (OUI): This 24-bit number
identifies the manufacturer of the NIC. The IEEE assigns OUIs to NIC
manufacturers.
Vendor-assigned address: This 24-bit number uniquely identifies
the Ethernet hardware.Figure 16-6 MAC Address Components