The unique ID in MAC is 24 bits long which gives an option of 16.7 million unique IDs. The manufacturer will have much more than 16.7 million devices in the world. So how is the unique ID achieved?
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You have just explained it yourself. Each manufacturer has enough id's that it's not a problem.– RamhoundJan 31, 2014 at 3:39
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16.7 Million for one manufacturer is not sufficient to cover all network devices in the world.– SatishJan 31, 2014 at 3:41
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1Except there are 281,474,976,710,656 addresses. The address space is not 24-bit. EUI64 exists when the 281 trillion addresses isn't enough. All of this comes from IEEE documents.– RamhoundJan 31, 2014 at 3:45
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1 Answer
MAC addresses are six bytes (48 bits). That means there are 248 = 281,474,976,710,656 possible addresses.
Additionally, they are assigned in groups to manufacturers. The first three bytes are the OUI, or organisationally unique identifier, which each manufacturer is assigned. From those 2^24 = 16,777,216 addresses, the manufacturer is free to assign them as they wish.
As there are not 16.7 million manufacturers of NICs, a manufacturer is certainly free to request another block (for $2500) when it has depleted its pool.
The OUI database is publicly accessible here.
Another note: MAC addresses really only need to be unique within a local subnet. A MAC address is only used to talk to devices on the same broadcast domain - otherwise traffic is routed at the IP layer.
answered Jan 31, 2014 at 4:35
