but on the Debian domU it's eth16, after each reboot or shutdown it's a different interface number.It's the linux kernel which decide the if's name in this case. I don't know what rules it uses for this but I find it strange that it doesn't always pick up the same name.
[snip]
It's try to run on nonexistent interface, because each time it's different. I can define the interface e.g. eth10 and it's works on domU, but on next reboot is the interface number eth11 and the eth10 not found.
That sounds suspiciously like it's tied to the underlying domain ID (and hence the xvif pair). Does the number after eth correspond to the VM's ID in "xm list"?
-- Stephen