nanog mailing list archives
Re: what about 48 bits?
From: James Hess <mysidia () gmail com>
Date: Sun, 4 Apr 2010 17:34:33 -0500
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
Current thread:
- Re: Hubs on a NIC (was:Re: what about 48 bits?), (continued)
- Re: Hubs on a NIC (was:Re: what about 48 bits?) Steven Bellovin (Apr 07)
- Re: Hubs on a NIC (was:Re: what about 48 bits?) Joe Greco (Apr 08)
- Re: Hubs on a NIC (was:Re: what about 48 bits?) Roland Perry (Apr 08)
- Re: what about 48 bits? Michael Thomas (Apr 07)
- Re: what about 48 bits? Michael Thomas (Apr 07)
- Re: what about 48 bits? Roland Perry (Apr 08)
- Re: what about 48 bits? A.B. Jr. (Apr 04)
- Re: what about 48 bits? Scott Howard (Apr 04)
- Re: what about 48 bits? Larry Sheldon (Apr 04)
- Re: what about 48 bits? Kevin Oberman (Apr 04)
- Re: what about 48 bits? Valdis . Kletnieks (Apr 05)
- Re: what about 48 bits? Patrick W. Gilmore (Apr 05)
- Re: what about 48 bits? Valdis . Kletnieks (Apr 05)
- Re: what about 48 bits? joel jaeggli (Apr 05)
- Re: what about 48 bits? Jon Lewis (Apr 06)
- Re: what about 48 bits? Mark Smith (Apr 04)
- Re: what about 48 bits? Jim Burwell (Apr 04)