Comment 13 for bug 673705

Quoting Derek Simkowiak (<email address hidden>):
> This bug is probably a duplicate issue as this:
>
> https://bugs.launchpad.net/ubuntu/maverick/+source/qemu-kvm/+bug/584048
>
> The problem is with Linux bridging. When adding or removing a MAC
> address (like for KVM, VirtualBox, or even LXC) then if the bridge
> changes its MAC, this symptom happens. See comment #60 at the URL
> above, and also see this:
>
> https://www.redhat.com/archives/libvir-list/2010-July/msg00450.html
>
> The workaround is to use a MAC address that starts with "fe" (or any
> high really high number) for your guests. This causes the kernel to
> default to the hardware MAC for the bridge.

Derek, thanks so much for this. You're almost 100% correct. I had even
suspected that bug (in comment #7), but I failed to make the simple
connection explaining this behavior.

The proposed solution does *not* suffice, and in fact I just reproduced
the bug in natty!

The current solution counts on the bridge being associated with a physical
NIC. But our default configuration uses a NAT bridge which starts with
no physical devices attached. So it starts with a zero-ed out mac addr.
Then every time you start a VM with a lower MAC address than the first
VM's, you can see this pause. And if you shut down the VM with the
lowest MACADDR, you'll again see the pause.