odd bhyve <-> ubuntu 14.04 problem

[John]

Hello list,

I upgraded the host from freebsd-10-RC3 to 10.1-R and after that 
upgraded bhyve to grub2-bhyve-0.30 today and since then I've found that 
when booting ubuntu 14.04.1 LTS guests, the ethernet interface (ethN 
where N is a number) is now variable. This is an issue because if I stop 
a VM and say reboot the host, I have to hack about with the VM instead 
of just booting it.

Previously the VM always saw the virtual network interface as eth0. Now, 
it's anything but that. bhyve has been upgraded, the VM hasn't. How can 
I control this behaviour? I want eth0 to remain as eth0. These are all 
VMs that were eth0 before the bhyve upgrade. It doesn't appear to matter 
what tap interface is used. I don't have this issue with freebsd guests 
on the freebsd host, just ubuntu 14.04.1 LTS.

I define the bridge and 9 tap interfaces at boot, in case this is 
relevant. Please can anyone shed some light?

thanks,

-- 
John