MAC address

The data link layer is used for moving information between two hosts in a local area network. If several nodes share the same medium, access must be controlled. To avoid confusion, every network interface device is assigned a unique media access control (MAC) address.

The manufacturer assigns the MAC at the factory, and also bundles driver software with the network interface hardware. The MAC address allows us to locate a specific machine within a network.

The MAC address is 48 bits long. The 24 high order bits identify the vendor and the 24 low order bits are the device serial number.

For example, the MAC address of the wireless Ethernet adapter on my computer is 00-06:5B-BC-7A-C7. The 00-06-5B designates Dell Computer Corporation and the BC-7A-C7 is the serial number of the device.

You can find the MAC addresses of the network interface devices in your computer with the ipconfig /all command. Once you have the MAC address, you can determine the manufacturer at http://coffer.com/mac_find/, for example: 

Search results for "00065b"
   MAC Address
   Prefix         Vendor
   00065B       Dell Computer Corp.

Search results for "dell"
   MAC Address
   Prefix         Vendor
   00065B       Dell Computer Corp.
   000874       Dell Computer Corp.
   00B0D0       Dell Computer Corp (was: Computer Products International)
   00C04F       Dell

The address resolution protocol (ARP) is used to find the MAC address corresponding to a given IP address and the reverse address resolution protocol (RARP) supplies the IP address given the MAC address of a device.

Note that if a computer has more than one network interface device (for example, both wireless and wired Ethernet interfaces) it will have multiple MAC addresses.

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