Mac – How is the MAC address on a computer determined

mac addressnetworking

While imaging some computers today, I started to wonder… what if two LAN MAC addresses on two different computers matched?… That would cause some problems. I later came to understand that the MAC address' 48-bit address space contains potentially 248 or 281,474,976,710,656 possible MAC addresses. [ in other-words, a lot of networking devices ]

How are these MAC addresses determined?

Will we ever run out of them? ( I know the second question is speculation, but there are a lot of devices that require a mac addresses…)

Do MAC addresses get recycled?

Best Answer

  1. The MAC is broke into two parts; the OUI (1st 24 bits) and the device ID (last 24 bits). The IEEE controls and allots the OUI portion; so if you got into the business of making your own NICs you would have to register with the IEEE and get your own unique OUI. The device ID portion is administered freely by the company.

  2. We could very well run out, but a MAC address only needs to be unique across an individual layer 2 network.

  3. The OUI portion is not something that is recycled, if you are poking around in your switches MAC address table you can tell by the first 24 bits who made the device, such as Cisco, Google "OUI lookup".

I am sure that individual manufacturers probably recycle their MACs, just so as long as those two NICs never end up on the same layer 2 network then it would be fine.

Network administrators can even choose to use locally administered MAC addresses.