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Re: overriding udev rules

On Sat, 2013-08-24 at 12:34 +0200, Thomas Goirand wrote:
> On 08/22/2013 03:12 AM, Peter Samuelson wrote:
> > 
> > [Thomas Goirand]
> >> Oh ok. Not useful at all if you ask me. Why? Because sometimes, you
> >> can't change the MAC address. For example, if you use the OpenStack
> >> bare metal driver, then you continue to use virtual machine images,
> >> though they will be used on a real hardware where you can't change
> >> the MAC address.
> > 
> > So you're saying, when your NIC is tied to actual physical hardware,
> > udev behaves as though it is tied to actual physical hardware.
> No. I'm saying that udev is making the wrong assumption that virtual
> machines are only bound to a specific MAC address range, when this is
> not at all the reality, for example when using read hardware for running
> cloud applications.

There is a specific MAC address range for locally administered
addresses, and it's very large indeed - everything with the 7th bit set 
(i.e. (addr[0] & 2) == 2).  Which is the main thing udev checks for:

ENV{MATCHADDR}=="?[2367abef]:*",	ENV{MATCHADDR}=""

(after white-listing some manufacturer screw-ups).

> You can't tell that my usage is wrong, and the software is right.
> Software should be adapted to use cases, and not the opposite way.

There is a very clear standard that distinguishes globally and locally
administered addresses.

While you would possibly to buy your own OUI and make global assignments
to your VMs, I seriously doubt you are doing that.  Don't steal address


Ben Hutchings
Never put off till tomorrow what you can avoid all together.

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