Q: What is a hardware address?
A: It is the unique hexadecimal serial number assigned to each Ether- net network device to identify it on the network. With Ethernet devices (as with most other network types), this address is permanently set at the time of manufacture.
Q: Why does the Networking and Ingtegration Department want to know the ethernet hardware address associated with my network card?
A: Your hardware address is a very important piece of information to the UHMC NID. Since this is a hardware address is a unique number, this is a very easy way for the NID to indentify different computers on the network. Along with network troubleshooting and monitoring the NID assigns your computer its IP address based on this hardware address.
Q: Why must the hardware address to be unique?
A: Each card has a unique hardware address, so that it will be able to exclusively grab packets off the wire meant for it. If the hardware addresses are not unique, there is no way to distinguish between two stations. Devices on the network watch network traffic and look for their own hardware address in each packet to determine whether they should decode it or not. Special circumstances exist for broadcasting to every device.
Q: Is there a special numbering scheme for hardware addresses?
A: The hardware addresses are exactly 6 bytes in length, and are usually written in hexadecimal as 12:34:56:78:90:AB (the colons may be omitted, but generally make the address more readable). Each manufacturer of Ethernet devices applies for a certain range of hardware addresses they can use. The first three bytes of the address determine the manufacturer. RFC-1700 lists some of the manufacturer-assigned hardware addresses. A more up-to-date listing of vendor hardware address assignments is available on ftp.lcs.mit.edu in pub/map/Ethernet-codes.
(sections of this document were taken from the Ethernet Network Questions and Answers which is summerized from the UseNet group comp.dcom.lans.ethernet.)