Re: [libvirt-users] Fake Network Interface

From: "Laine Stump" <laine(a)laine.org&gt; To: libvirt-users(a)redhat.com Cc: "Andrew Martin" <amartin(a)xes-inc.com&gt; Sent: Tuesday, January 14, 2014 3:54:51 AM Subject: Re: [libvirt-users] Fake Network Interface On 12/30/2013 11:25 AM, Andrew Martin wrote: > Is there a supported method for creating a fake network interface in a VM's > configuration file? I was using the below construct, however it is no > longer > working for me in recent versions of libvirt (libvirt 1.0.2 with qemu-kvm > 1.4.0). I assume this wasn't working for you either because you previously had a network named "fake" in your config, and that network wasn't present when you tested with the newer libvirt, or because the <address> element created a conflict with an existing device on the same guest that was already using the same slot? > Is there a different, preferred method for creating a fake virtual > interface on the guest which does not exist on the host? > <interface type='network'> > <mac address='aa:aa:aa:aa:aa:aa'/> > <source network='fake'/> > <address type='pci' domain='0x0000' bus='0x00' slot='0x03' > function='0x0'/> > </interface> On 01/14/2014 12:54 AM, Andrew Martin wrote: > I found the answer to this question: > 1. create an XML file with a fake configuration (including a subnet not in > use elsewhere): > <network> > <name>fake</name> > <bridge name='virbr1' stp='on' delay='0' /> > <ip address='192.168.0.1' netmask='255.255.0.0'></ip> > </network> 1) you don't need to (and probably shouldn't) specify the <bridge> element when defining the new network - libvirt will autogenerate a unique bridge name if one isn't provided, and stp defaults to on with a delay of 0 anyway. 2) If this network is just a parking place, then you don't need to specify an <ip> element either. This will save you from having an extra dnsmasq instance started on the host to answer dns queries to 192.168.0.1 (and has the added advantage that a guest will be unable to use this "parked" network connection to erroneously communicate with the host). In other words, all you really need in the XML file is this: <network> <name>fake</name> </network> > > 2. define the network: virsh net-define /path/to/fake.xml > 3. autostart the network: virsh net-autostart fake > 4. start the network now: virsh net-start fake > > Once done, you can add this block of XML to your VM config with "virsh edit > <vm_name>": > <interface type='network'> > <mac address='aa:aa:aa:aa:aa:aa'/> > <source network='fake'/> > <address type='pci' domain='0x0000' bus='0x00' slot='0x03' > function='0x0'/> > </interface> > Note that you should adjust the "slot" and "mac" arguments to avoid > conflicts. It's actually easier and less error prone to just omit the <mac> and <address> elements completely - libvirt will auto-generate non-conflicting values for both if they aren't provided. So the interface xml would look like this: <interface type='network'> <source network='fake'/> </interface> (you may want to add a <model type='virtio'/> to use a better emulated device than the default rtl8139).