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Subject: Re: [Qemu-devel] net packet storms with multiple NICs
From: Mark McLoughlin <markmc@redhat.com>
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Date: Fri, 23 Oct 2009 17:43:38 +0100
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To: Michael Tokarev <mjt@tls.msk.ru>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, KVM list <kvm@vger.kernel.org>

On Fri, 2009-10-23 at 20:25 +0400, Michael Tokarev wrote:
> I've two questions:
> 
> o what's the intended usage of all-vlan-equal case, when kvm (or qemu)
>    reflects packets from one interface to another?  It's what bridge
>    in linux is for, I think.

I don't think it's necessarily an intended use-case for the vlan feature

> o why different -net guest -net host pairs are not getting different
>    vlan= indexes by default, to stop the above-mentioned packet
>    storms right away?  I think it's a wise default to assign different
>    pairs to different vlans, by counting -net host and -net guest
>    sequences.

With 0.12, we're going to be de-emphasising the vlan feature and instead
have NICs directly connected to host backends. The vlan feature will be
just another host backend, but optional

You'll start guests with e.g.:

  -netdev tap,id=tap.0 -device virtio-net-pci,netdev=tap.0

Cheers,
Mark.