what about 48 bits?

Jim Burwell jimb at jsbc.cc
Sun Apr 4 16:48:38 CDT 2010


On 4/4/2010 08:46, Jonathan Lassoff wrote:
> Excerpts from John Peach's message of Sun Apr 04 08:17:28 -0700 2010:
>   
>> On Sun, 4 Apr 2010 11:10:56 -0400
>> David Andersen <dga at cs.cmu.edu> wrote:
>>
>>     
>>> There are some classical cases of assigning the same MAC address to every machine in a batch, resetting the counter used to number them, etc.;  unless shown otherwise, these are likely to be errors, not accidental collisions.
>>>
>>>   -Dave
>>>
>>> On Apr 4, 2010, at 10:57 AM, jim deleskie wrote:
>>>
>>>       
>>>> I've seen duplicate addresses in the wild in the past, I assume there
>>>> is some amount of reuse, even though they are suppose to be unique.
>>>>
>>>> -jim
>>>>
>>>> On Sun, Apr 4, 2010 at 11:53 AM, A.B. Jr. <skandor at gmail.com> wrote:
>>>>         
>>>>> Hi,
>>>>>
>>>>> 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?
>>>>>
>>>>>           
>> Sun, for one, used to assign the same MAC address to every NIC in the
>> same box.
>>     
> I could see how that *could* work as long as each interface connected to
> a different LAN.
>   
That was a logic Sun used.  Every NIC would be connected to a different
subnet, so duplicate MACs shouldn't be a problem.  For the most part
this worked, but some situations required a unique MAC per NIC, and Sun
had a bit you could flip to turn this on.  I believe it was an OpenBoot
prom variable called "local-mac-address?" which you'd set to true if you
wanted it to use each NICs MAC instead of the "system MAC".

-Jim





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