Date: Tue, 23 Mar 2010 18:25:02 -0700
From: Ehud Gavron <gavron@wetwork.net>
Subject: Re: [PATCH V2] ssb: Implement virtual SPROM on disk
In-reply-to: <201003222325.35994.mb@bu3sch.de>
To: Michael Buesch <mb@bu3sch.de>
Cc: Larry Finger <Larry.Finger@lwfinger.net>,
	Calvin Walton <calvin.walton@gmail.com>,
	linux-wireless@vger.kernel.org, bcm43xx-dev@lists.berlios.de
Message-id: <4BA969EE.8000809@wetwork.net>
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References: <4ba6aa45.z5Wso1NMth9eMeFG%Larry.Finger@lwfinger.net> <1269239303.12836.17.camel@ayu> <4BA7E79C.9070100@lwfinger.net> <201003222325.35994.mb@bu3sch.de>
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Michael Buesch wrote:
> On Monday 22 March 2010 22:56:44 Larry Finger wrote:
>   
>> Does anyone have any suggestions on what characteristic could be used to
>> generate a unique MAC address for a box in a udev rule?
>>     
>
> /dev/urandom
>
> Yeah, there's the chance of clashes. In practice there won't be any clashes,
> however. If you think there's a real risk, you should start playing
> the lottery tomorrow. You'll immediately win a million dollars so you don't have
> to worry about those questions anymore. ;)
>
> In fact, I think the risk for mac clashes is not really reduced by generating the mac
> address from serial numbers, whatever, etc...
>
>   
DEC used the L3 address to encode a new MAC at the time the [L3] address was
set (DECnet v4).  The advantage was they didn't need to use the equivalent
of ARP.  Of course this is a violation of strict layer separation.

Octet1-Octet3 - Broadcom assigned MAC IDs.  I found the following:
00-05-B5
00-10-18
00-1B-E9
18-C0-86

Octet4-octet6 - Lowest three octets of the unixtime.


Advantages: for the local area network all TZ settings should be the same,
so the MAC addresses *will* be different.  Beyond the first router that 
won't
matter.  Also for the same machine different interfaces are GUARANTEED
to have different MAC addresses.

For two machines to have the same MAC they would have to be booted at
(same time x processing factor) such that the B43 initialization will 
result
in the same MAC address.  I'd like to think those odds are even lower than
your lottery.

A million dollars?  
http://www.active-domain.com/resources/million-dollar-domains.htm
Yeah got the t-shirt.


E


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