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Re: [Qemu-discuss] qemu guests using 802.1q vlans bridged on host

From: Stephan von Krawczynski
Subject: Re: [Qemu-discuss] qemu guests using 802.1q vlans bridged on host
Date: Thu, 22 Aug 2013 20:22:52 +0200

On Thu, 22 Aug 2013 11:55:28 -0600
Mike Lovell <address@hidden> wrote:

> On 08/22/2013 08:39 AM, Stephan von Krawczynski wrote:
> > Hello all,
> >
> > I'd like to do something very simple - at least that's what I thought ;-)
> > I want a guest to have access to a network just as if he was connected to 
> > the
> > real card, but set up as bridge on the host and virtio network driver. The
> > guest should be able to configure and use some or maybe even many 802.1q 
> > vlans
> > on this network and the traffic should go out tagged.
> >
> > So I setup the hosts bridge and connected an intel network card and a qemu
> > virtio card. Now the problem: No vlan-tagged traffic from the physical
> > interface reaches the guest at all, and no vlan-tagged traffic from the 
> > guest
> > reaches the physical net over the bridge. One major reason for this is the
> > vlan offloading by the host interface card (intel). Another seems to be that
> > arp requests are somehow not going through the bridge for the vlans.
> >
> > I hope that someone here has used 802.1q vlans inside guests before and can
> > share some tips how to make this work. Because out-of-the-box it does not. 
> > All
> > system are linux of course and with latest kernels (3.10.9 currently).
> > qemu is 1.5.2.
> > Thanks for any hints.
> i'm guessing that you are using the standard linux bridge and i believe 
> that would be the problem. i don't think it supports vlan tags at all. 
> you should try using openvswitch as the virtual switch connecting the 
> physical and guest interfaces. it supports vlans and tagging and i think 
> you will be able to get tagged vlans all the way to the guest interfaces 
> by using it.
> mike

I don't trust openvswitch regarding performance and latency. AFAIK linux
bridge combined with vhost_net is zero-copy, right?
What about openvswitch?


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