SparkFun Forums 

Where electronics enthusiasts find answers.

Everything ARM and LPC
By fll-freak
MAC is a unique hardware address. It is the lowest level identification of a computer network node. each Ethernet card is assigned a unique id number in the form of 6 hex digits. If you type iconfig or ifconfig into most computers command line, they will spit out the unique number. Some computers allow you to modify the MAC address, but most the address is hardcoded into the hardware by the vendor.
By n1ist
If you need to get one, Microchip sells small roms that come pre-programmed with a unique MAC address. For personal projects, I often use the one printed on an ethernet card in the scrap bin at work.
By stevech
You can use a self-assigned MAC address. The OUI (now EUI) numbering scheme has 2 or 3 bits in the most significant byte - that if set to the self-managed code, you can use whatever other bit patterns you wish. The only restriction is that such a self-administered MAC address cannot appear on the public Internet - which it wouldn't in all likelihood based on how you get Internet access.

If I recall correctly, its a 0x02 in the MSByte