Overview of Ethernet Addresses

Overview of Ethernet Addresses

You may remember from an earlier section that TCP/IP is independent of the underlying network hardware. If you are running on an Ethernet-based network, be careful not to confuse the Ethernet hardware address and the IP address required by TCP/IP.
Each Ethernet network card (and any other NIC, for that matter) has its own unique hardware address, known as the media access control (MAC) address. This hardware address is predefined
and preprogrammed on the NIC by the manufacturer of the board as a unique 48-bit number.
The first three bytes of this address are called the Organizationally Unique Identifier (OUI) and are assigned by the Institute of Electrical and Electronics Engineers (IEEE). Manufacturers
purchase OUIs and then vary the last three bytes of the MAC address for each interface they produce, making each address unique provided no other manufacturer makes unauthorized use
of the OUI and related address space. Remember that the Ethernet address