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Date:	Tue, 11 Dec 2007 21:36:59 -0800
From:	Stephen Hemminger <>
To:	Herbert Xu <>
Cc:	Andrew Morton <>,,,,
	Jeff Garzik <>,
	"Rafael J. Wysocki" <>
Subject: Re: [Bugme-new] [Bug 9545] New: Cannot bring up a bridge interface
 without a MAC address set

On Wed, 12 Dec 2007 09:51:05 +0800
Herbert Xu <> wrote:

> On Tue, Dec 11, 2007 at 02:52:43PM -0800, Stephen Hemminger wrote:
> >
> > The tap devices have to have addresses don't they. So bringing up an empty
> > bridge is meaningless. If you just add the device first then it will work.
> Actually bringing up a bridge with no constituents is useful for
> a bridge that's made up of only virtual interfaces.  Since each
> vritual interface may be created or destroyed at run-time it'd
> be quite awkward to check every time to see if that's the last
> or first and act differently on the bridge.
> More importantly constiuents can be added to and removed from a
> bridge without taking it down.
> > Could be fixed to prevent errors from existing scripts but it is not a complete showstopper.
> Well this stops FC8 working with Xen so for that it's a showstopper :)
> > The problem is that when device is brought up it propogates events up to
> > other layers and applications, these layers will then query and see a bogus
> > address.
> What exactly would it break for this scenario though?

Well with earlier kernels, ipv6 and others would see an invalid address (all zeros).
That could be a problem if some netlink watching program or udev script
propagated that value into a database or management interface. But now
using a random value, that won't happen.

Stephen Hemminger <>
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