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Date: Wed, 28 Oct 2009 10:34:29 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] accidental mistyping of command line kills networking
Message-ID: <20091028083429.GS29477@redhat.com>
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To: Avi Kivity <avi@redhat.com>
Cc: Beth Kon <eak@us.ibm.com>, qemu-devel <qemu-devel@nongnu.org>

On Wed, Oct 28, 2009 at 08:29:42AM +0200, Avi Kivity wrote:
> On 10/27/2009 11:44 PM, Anthony Liguori wrote:
> >
> >It's actually not okay.  You're creating a bridge with two tap
> >devices on the bridge that happen to be connected in qemu by a
> >vlan.  If one tap device receives a packet, qemu is going to
> >forward that packet to the other tap device, which will in turn
> >send the packet to the bridge which in turn sends it to the first
> >tap device.
> >
> >Resulting in an infinite networking loop.
> >
> 
> It shouldn't kill networking though.  If a guest has two nics
> connected to the same host bridge (a reasonable configuration), and
> then connects these two nics through its own bridge, it creates the
> same sort of loop.  If that kills networking, we have a
> guest-initiated DoS (not that the userspace-initiated DoS was much
> better).
> 
That's what STP is for.

--
			Gleb.