On Wed, 3 May 2000, Bernd Markgraf wrote:
>> Isn't there a problem with this in that it is possible (although not
>> necessary all that likely) for two nics to have the same MAC address?
>iirc, mac adresses are unique! thats how we identify nic world wide. it's
>a mix of manufacturer, type and serial number. so there is no problem
>unless you try to burn the nic's prom yourself ;-)
No, they are NOT unique. They _are_ "relatively unique" -- which is to say
the manufacturer sequentially numbers the MAC when the card is ready to
leave the plant (i.e. after QC, etc.) Eventually, the counter will roll
over -- how many NICs has 3Com and Intel made?
Additionally, the MAC is "just another number." In almost all cases, the
MAC address can be changed -- after all, the manufacturer had to be able
to set it following construction. AND, sparc hardware doesn't have a MAC
address as part of the NIC -- it's part of the _machine_ of all things.
The SunOS/Solaris 'ifconfig' has had a "macaddr" option for a long time:
To change the Ethernet address for interface le0, use the
following command:
example% ifconfig le0 ether aa:1:2:3:4:5
The MAC address only has to be unique per cable segment.
--Ricky
PS: The odds of someone purchasing two NICs in his/her lifetime with the
same MAC address (baring tampering) is _very_ low.
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