MAC Address
Last updated: 2/2/02

Q.  What is an Ethernet  MAC address?

A.  MAC = Media Access Control.  Each and every Ethernet device interface to the network media (e.g., network adapter, port on a hub) has a unique MAC address, which is "burned" into the hardware when it is manufactured.  MAC addresses uniquely identify each node in a network at the Media Access Control layer, the lowest network layer, the one that directly interfaces with the media, such as the actual wires in a twisted-pair Ethernet.  In modern Ethernets the MAC address consists of six bytes which are usually displayed in hexadecimal; e.g.,

00-0A-CC-32-FO-FD

The first three bytes (e.g., 00-0A-CC) are the manufacturer's code and can be used to identify the manufacturer.  The last three are the unique station ID or serial number for the interface.  One can determine the MAC address of an operating Network Interface Card (NIC or network adapter) in Windows 9X/Me with Start, Run, enter winipcfg, and select the adapter.  In Windows NT, 2000, and XP it can be determined by opening a DOS Window/Prompt (Start, Programs, Accessories...) and typing:

C:\>ipconfig /all

The MAC address/station ID may be printed on the NIC.

Many broadband routers can clone a NIC MAC address.  That is, make the Wide Area Network (WAN) Ethernet interface going to a cable or DSL MODEM look like a NIC in a PC.  This is useful in that many MODEMs marry themselves to a specific MAC address when they are first installed and it can be rather difficult to get them to marry themselves to a new MAC address.  The WAN port MAC address on some routers can be manually changed (e.g., the SMC7004ABR).

It is possible to change/override  the MAC address with Windows, etc.

A vendor/Ethernet MAC address lookup service is available at
http://coffer.com/mac_find/.