MAC Addresses

The MAC, or Media Access Control Address, is one of the most vital identity elements in computer networking.

Every addressable network device, be it a managed switch, modem, network card, or router, is assigned a unique address when it is manufactured. The MAC address has a format

xx-xx-xx-xx-xx-xx

where each "x" is a hexadecimal character. The string of 12 hexadecimal characters is assigned, intentionally, by the manufacturer, to prevent duplication by any other networked device, either now, or in the future.

Some misguided persons believe that changing the MAC address of their computer (network card) is a way to hide themselves, or to change their identity at will. This is an erroneous assumption, and can lead to worse problems.

• You absolutely must have a unique MAC address on all networked devices, in any connected network. If you go changing this identity element, and cause a conflict, you could cause yourself and other people grief.
  
• If you change your MAC address in an attempt to change your IP address on a public Internet service, you could cause pain for a few people, including another subscriber, and the ISP. Changing your IP address is yet another form of Security by Obscurity.
  
• Note the MAC addresses do not pass between routed network segments, they are only seen by other hosts on the same subnet. It's possible that, if you setup a network device on your computer with a phony MAC address, that's unique on your subnet, one day you may carry that computer to a network where that address is legitimately in use. Either your computer, or the legitimate owner of the address (and probably both) will suffer from your hijacking of that address.

There is one specific situation where your MAC address should be changed. In any other situation, changing the MAC address just isn't a valid solution.

If you need to associate a MAC address with its vendor, the IEEE OUI / Company_id Assignments database can be searched for this information.