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A MAC address is made up of 12 bytes. For example: 00-80-C8-E3-4C-BD. Of this address, the first 6 bytes (00-80-C8) identifies the card's manufacturer. The IEEE is the body that assigns manufacturers their IDs, called Organizationally Unique Identifiers. So, this leaves 6 bytes which can be assigned by the manufacturer to be unique to that manufacturer. So, each manufacturer can have 16,777,215 different unique ID's for their cards (00-00-00 to ff-ff-ff). There are some unique MAC addresses though such as all broadcast ff-ff-ff-ff-ff-ff or different multicast MAC's 01-00-5e-00-00-00 through 01-00-5e-7f-ff-ff. So, really with the number of manufacturers and unique addresses, does it seem like running out of MAC addresses is realistic?
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Fresh | Mar 25 2008 4:16PM GMT
Yeah well, I don’t think its possible…not in our lifetime anyway. But hypothetically speaking, If we did run out, what would happen?? Besides, word on the streets says even with that number of addresses, we’ll be running out by 2100.
Labnuke99 | Mar 26 2008 8:36PM GMT
Sounds like some confusion between IP addresses and MAC addresses? Do you have any references for the 2100 date you mention?
Jmkelly | Mar 26 2008 11:48PM GMT
Rich Seifert (one of the developers of Ethernet) used to say that the entire crust of the planet could be turned into 802.11 devices before we’d run out of MAC addresses. Presumably he ran the numbers — I know I didn’t!
Fresh | Mar 27 2008 4:38PM GMT
“The IEEE expects the MAC-48 space to be exhausted no sooner than the year 2100″, <a href="http://en.wikipedia.org/wiki/MAC_address." rel="nofollow">http://en.wikipedia.org/wiki/MAC_address.</a>
“IEEE expects MAC-48 space to be exhausted around the year 2100 by which time….”, <a href="http://www.cs.umn.edu/help/network/mac.php" rel="nofollow">http://www.cs.umn.edu/help/network/mac.php</a>
Labnuke99 | Mar 28 2008 1:26PM GMT
Thanks for the link/reference. It does sound like there is a plan to go to EUI-64 addresses to cover the risk of running out of 281,474,976,710,656 addresses. The EUI-64 is part of the IPv6 plan according to the referenced article. So, they (IEEE and manufacturers) have thought through this issue.
