You most definitely do not need to destroy and re-create a VM just to
add a 2nd network interface.
I don't think those vnet interfaces got created by the host OS. I
believe those are created by KVM (or libvirt) when you start a VM. I
could be wrong though. But I just checked on my CentOS 6 KVM host
machine and I see as many vnet interfaces as many VMs are currently
running (or if one VM has two virtual network cards then of course that
VM results two vnet interfaces shown on the host). Here the relevant
part from one such VM's XML file (those XML files are under the
/etc/libvirt/qemu directory on my CentOS host ) :
<interface type='bridge'>
<mac address='00:16:36:e2:20:ea'/>
<source bridge='br0'/>
<model type='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03'
function='0x0'/>
</interface>
<interface type='bridge'>
<mac address='00:16:36:e2:20:eb'/>
<source bridge='br600'/>
<model type='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06'
function='0x0'/>
</interface>
As you can see, there are two interfaces defined in this VM's XML file.
One is connected to the host's br0 interface and the 2nd is connected to
the host's br600 interface. You must make sure that all your mac
addesses are unique on your network though!!
After editing a VM's XML file with your favorite editor, you need to
execute this command:
virsh define /etc/libvirt/qemu//your-vm-name/.xml
or just simply use this editor:
virsh edit /your-vm-name/
(but I hate vi, so I use my favorite editor and when I finished editing
I just run virsh define.)
I edited VM's XML files many times and I can add/remove virtual network
cards without problems.
Zoltan
On 12/9/2015 9:55 AM, Howard Leadmon wrote:
Tried that as well, but this has to be something that gets set at the
OS level and loaded, as if you look at dmesg output, you can see all
the vnet?? nodes as the OS comes online. So the question is, what
is virt-install doing that creates the needed vnet interface that is
part of the bridge. I really had to kill and reload the VM just to
load a second interface..
---
Howard Leadmon
*From:*[email protected]
[mailto:[email protected]] *On Behalf Of *Zoltan Frombach
*Sent:* Wednesday, December 9, 2015 2:42 AM
*To:* Discussion about the virtualization on CentOS
<[email protected]>
*Subject:* Re: [CentOS-virt] How to manually add a new interface to a
bridge device?
I would stop the VM, edit its definition file (that's an XML file) and
then start it up. But be careful: After you edit the XML file, you
need to execute a command so KVM re-reads that file. I forgot that
command, but you can look it up on Google.
On Dec 9, 2015 7:52 AM, "Howard Leadmon" <[email protected]
<mailto:[email protected]>> wrote:
Maybe my google-fu is failing me, but I have spent the past couple
hours looking at how to add a vnet? Device to my KVM host running
CentOS 6, and for the life of me I can’t get this going.
From all my research if I want to add a device I should just do
‘brctl addif br1 vnet14’ if I want to add a vnet14 to bridge
br1. When I do this, I get:
# brctl addif br0 vnet14
interface vnet14 does not exist!
If I run a ‘brctl show’ I get the following:
# brctl show
bridge name bridge id STP enabled interfaces
br0 8000.00237dd22a4c no eth0
vnet0
vnet10
vnet11
vnet13
vnet2
vnet3
vnet4
vnet6
vnet8
br1 8000.00237dd22a50 no eth1
vnet1
vnet12
vnet5
vnet7
vnet9
Needless to say the existing vnet?? Devices are in use on guest
VM’s currently.
When I create a new VM using virt-install, I usually add the
following to my command line:
--network=bridge:br0 --network=bridge:br1
I messed up building a new VM, and only added the br0 interface to
the VM, but need the br1 interface as well. So my question is, or
a pointer to how I can add that br1 interface to my existing VM,
and create the needed vnet14 interface for it to attach to?
If anyone can explain how to do this, or give me a good pointer on
where the info is on how to do this, it would sure be a huge help..
Thanks…
---
Howard Leadmon
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