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Re: [Xen-users] uniq mac address generator

  • To: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
  • From: "James Youngman" <jay@xxxxxxx>
  • Date: Sat, 14 Apr 2007 21:42:11 +0100
  • Cc: trilok nuwal <tc.nuwal@xxxxxxxxx>, Xen list <Xen-users@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Sat, 14 Apr 2007 13:40:56 -0700
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  • List-id: Xen user discussion <xen-users.lists.xensource.com>

It only needs to be unique to your local network

Not always true, really.   For example if you run software thar
generates version-1 UUIDs you could create yourself a lot of difficult
to solve problems (and possibly cause data corruption) by assuming
that.  See for example

- anything outside that
will not be using MAC addresses to determine the routing of the packet
anyways [AFAIK]

MAC addresses don't determine routing anyway, they're at the wrong link layer.

so it's meaningless to aim for uniqueness outside your
own network (although it is of course practical to know that ALL MAC
addresses used in the entire known world are unique).

Quite a bit of software assumes this, and will do the wrong thing in
very subtle ways if this assumption is not true.  But the chances of
getting bitten by this bug are quite small.

Of course, if you're on a large corporate network, you may still have
the problem that someone else uses the same easymac script to generate
MAC addresses...

True.   And Ethernet card manufacturers have been known to ship
Ethernet cards with conflicting MAC addresses anyway.


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