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Date: Wed, 14 Oct 2009 19:20:40 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [Qemu-devel] Re: [PATCH-updated] qemu/net: add raw backend
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To: Jamie Lokier <jamie@shareable.org>
Cc: Or Gerlitz <ogerlitz@voltaire.com>, Arnd Bergmann <arndbergmann@googlemail.com>, qemu-devel@nongnu.org

On Wed, Oct 14, 2009 at 05:54:47PM +0100, Jamie Lokier wrote:
> Michael S. Tsirkin wrote:
> > > The fact that network manager does work well with bridged interfaces is  
> > > a network manager bug.
> > 
> > Network manager was just one example.
> 
> Even if network manager and all other configuration programs are fixed
> to handle a bridge, it's still quite fiddly to configure them.
> 
> I find I have to use
> 
>    - bridges to an uplink interface for some VMs (guest has IP on same
>      network as host, fixed host interfaces, typically in servers)

Another similar setup of interest is when you have dhcp server and want
both VMs and host to get IP from there.


>    - bridges attached to changing uplink for some VMs (laptop, where
>      the main internet uplink changes between eth0/wlan0/ppp0/bnep0
>      according to available signals)
> 
>    - no bridge at all (just routing tap, used on all sorts of machines)
>      for VMs needing to run on host-local IPs and talk to the host,
>      and maybe NAT to the internet
> 
>    - bridges not attached to any host interface, just multiple tap
>      interfaces, used to connect guests with host-local IPs that must
>      see each other's broadcasts
> 
> The corresponding iptables is rather tricky too.

Another issue is that host will often lose networking while you fiddle
with bridge connected to an uplink.  So doing this if your only way to
access the box is through the network is tricky.


> > > It's getting fixed so in the near future, tap will satisfy all of
> > > these requirements.
> 
> That will be really nice if it does.
> 
> -- Jamie