Finding out the location order of tap interfaces in KVM VM (Libvirt)

Question

I have inserted 8 tap interfaces in a Cisco Libvirt xml file that will create a guestmachine running Ciscio iOs image:

<interface type="ethernet">
  <start mode="onboot" />
  <target dev="cisco-89" />
</interface>
<interface type="ethernet">
  <start mode="onboot" />
  <target dev="cisco-90" />
</interface>
<interface type="ethernet">
  <start mode="onboot" />
  <target dev="cisco-91" />
</interface>
<interface type="ethernet">
  <start mode="onboot" />
  <target dev="cisco-92" />
</interface>
<interface type="ethernet">
  <start mode="onboot" />
  <target dev="cisco-93" />
</interface>

etc

However, what I want to find out is, when I boot up the Cisco iOs image and type show interfaces summary, it gives me a list of:

GigabyteEthernet1 GigabyteEthernet2 GigabyteEthernet3 etc

How do I know which tap device is assigned to which GigabyteEthernet inside the guestmachine?

Do I assume that cisco-89 corresponds to GigabyteEthernet1?

Thanks in advance

score 0 · Answer 1 · answered Sep 06 '13 at 23:00

Generally, the order in which the taps are created is the PCI bus order in which they get attached to the VM. If IOS (and this is something I don't know) sets up ordering according to the way it detects devices on the PCI bus, then the order will match, if not, it might end up being random on every reboot.

The only means of testing I can think of it to run traffic through a specific interface and watch the traffic stats on the hosts

Finding out the location order of tap interfaces in KVM VM (Libvirt)

1 Answers1