Starting at Ubuntu 16.04 and Debian 9 (daily builds so far), the network interfaces changes on both OSes.
In previous releases, both Debian and Ubuntu used to use old network naming mechanism, and on this new releases, the new ifname mechanism is being used, so, if you upgrade to these new version, the system may have the network unconfigured.
Now, the interface name from within a KVM guest moved from ethX to ibmvethX.
This is a change I did on my Debian /etc/network/interfaces file:
— interfaces.old 2016-05-16 10:09:32.530876729 -0400
+++ interfaces 2016-05-16 09:44:48.507722181 -0400
@@ -8,5 +8,5 @@ auto lo
iface lo inet loopback
# The primary network interface
-iface eth0 inet dhcp
+iface ibmveth0 inet dhcp
There are some configurations you should do on this mechanism if you wish to do device hot plug, as described in the ppc64el Ubuntu wiki page.