[124761] in North American Network Operators' Group
Re: what about 48 bits?
daemon@ATHENA.MIT.EDU (James Hess)
Sun Apr 4 18:35:25 2010
In-Reply-To: <i2x25f9e2131004040753k31515650xc28df222a4abf88e@mail.gmail.com>
Date: Sun, 4 Apr 2010 17:34:33 -0500
From: James Hess <mysidia@gmail.com>
To: "A.B. Jr." <skandor@gmail.com>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Sun, Apr 4, 2010 at 9:53 AM, A.B. Jr. <skandor@gmail.com> wrote:
> Lots of traffic recently about 64 bits being too short or too long.
> What about mac addresses? Aren't they close to exhaustion? Should be. Or it
> is assumed that mac addresses are being widely reused throughout the world?
> All those low cost switches and wifi adapters DO use unique mac addresses?
Hardware MAC-48 addresses are not assigned based on a network
topology. The first 24 bits are used for OUI which is an ID number
applied for [and paid for] by a manufacturer of network devices, the
2nd LSB of the most significant byte is reserved for 'local vs
universal administration flag', and the LSB of the most significant
byte is reserved for unicast/multicast flag. The bottom 24 bits
are assigned by manufacturer.
So there are 22 bits of usable global unicast OUIs, that is
4,194,304 possible.
and each OUI has 16,777,216 MAC address numbers.
Of the possible OUIs, only 13,557 are currently listed as allocated
in the IEEE OUI listing.
http://standards.ieee.org/regauth/oui/index.shtml
So a theoretical maximum of 227,448,717,312 unicast MAC addresses
could be globally assigned today (which is a vast overestimate,
assuming all presently assigned OUIs are already completely
exhausted). Out of 70,368,744,177,664, that is what, 0.3% ?
--
-J
