[CentOS-virt] proper bridging technoque

Thu Nov 21 22:36:03 UTC 2013
Digimer <lists at alteeve.ca>

On 21/11/13 17:32, aurfalien wrote:
> On Nov 21, 2013, at 2:24 PM, Digimer wrote:
>> I'm not sure what you are asking.
>> You should not see the vnetX devices from the VM (or even the VM's
>> definition file). They're created as needed to link the VM's interface
>> to the bridge. Think of them as simple network cables.
>> Some of the formatting isn't showing well on my mail client (text only),
>> so I am having a little trouble parsing some of the data...
>> If the VMs are using br6, then you see that it's already at 9000, so you
>> should be able to use 9000 from inside the VM as well. Trick is, the
>> vnetX devices are connected to the br0 bridge instead, which is set to
>> 1500 because eth0 is still 1500. So at this point, the VMs are
>> traversing br0, not br6.
>> As for 'virbr0', that is libvirtd's default NAT'ed bridge. I don't
>> recommend using those. I usually destroy them, personally.
>> So to fix your problem, you need to tell the VMs to use br6. If you want
>> to use jumbo frames on br0, you need to increase the MTU of eth0.
>> Remember that the bridge will use the MTU of the lowest connected device.
> So far my current VMs that work, I see there network as;
> Host device vnet 0 (Bridge 'br0')
> I do not see a;
> Host device vnet# (Bridge 'br6')
> My ints of interest are set to jumbo so thats not a prob.  I think the prob is that I am missing the vnet bridge device for eth6.
> So I'm curious why its not there and how do I create it?
> - aurf

I can't speak to the tools you are using, but I can say that this is
where the bridge is defined in the VM's XML definition file:

[root at an-c05n01 ~]# cat /shared/definitions/vm01-win2008.xml |grep vbr
-B 2 -A 5
    <interface type='bridge'>
      <mac address='52:54:00:8e:67:32'/>
      <source bridge='vbr2'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03'

Try changing: <source bridge='br0'/> -> <source bridge='br6'/> and
restart the VM.

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