libvirt users - Aug 2012 - network settings for an isolated network

Hi,

I try to configure a kvm with a NIC, but no attached network to this
NIC.

I tried following methods:

1. Create a generic ethernet connection 

I configured the VM with following interface section:
<interface type='ethernet'> 
     <script path='/root/noscript.sh'/>
     <target dev='myvm_nic0'/>
<interface/>


The script /root/noscript.sh exists and is executable and has only an
exit 0 statement. When I try to start the VM, virsh aborts with
following error:

error: Failed to start domain myvm
error: internal error process exited while connecting to monitor:
qemu-kvm: -netdev tap,script=/root/noscript.sh,id=hostnet1: could not
configure /dev/net/tun (tap%d): Operation not permitted
qemu-kvm: -netdev tap,script=/root/noscript.sh,id=hostnet1: Device 'tap'
could not be initialized


The tun module is loaded and I can create tap devices with tunctl. So
there might be no problem...




2. I configurerd a network with no forward element.

I've defined and started following network on the host with virsh
net-define / net-start
<network>
       <name>myvm_isolated</name>
       <bridge name='virbr_myvm_1' />
</network>

The documentation says: "If there is no forward element, the network
will be isolated from any other network (unless a guest connected to
that network is acting as a router, of course)."

The interface configuration of the domain was this:
<interface type='network'>
  <mac address='00:12:67:bb:bb:11'/>
  <source network='myvm_isolated'/>
  <model type='e1000'/>
</interface>


The VM starts as expected. But the interface is connected to an host
bridge like a NAT interface. There is a DHCP server in the network and
the VM gets an IP Address and can ping and ssh to the VM-Server...


I used following version of libvirt and qemu on SuSE Enterprise Linux
Server SP2:

# virsh version
Compiled against library: libvir 0.9.6
Using library: libvir 0.9.6
Using API: QEMU 0.9.6
Running hypervisor: QEMU 0.15.1



Can you please tell me how to configure a not connected (isolated)
network interface card for my VM?

Regards, 
Christian