Debian - network interface does not work any more after update / upgrade

After some search in the web ( god sake I have as well a laptop ) I figured out that some renaming of the network interfaces occurred ... so first thing to do: See which network interfaces currently are up ( for me only the Loopback was started )

sudo ifconfig

Now let's check the naming of all available network interfaces:

networkctl

For me the output looked like that:

WARNING: systemd-networkd is not running, output will be incomplete.

IDX LINK             TYPE               OPERATIONAL SETUP     
  1 lo               loopback           n/a         unmanaged 
  2 enp3s0           ether              n/a         unmanaged 
  3 enp4s0           ether              n/a         unmanaged

After that I took a look into /etc/network/interfaces ... which for me looks like that:

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# Comment in the right one (the one plugged in) otherwise system.d will run a startjob
#auto net0
#allow-hotplug net0
#iface net0 inet dhcp

auto net1
allow-hotplug net1
iface net1 inet dhcp

... you probably can guess what comes next ... replace net0 / net1 (or whatever you have there) by the LINKS listed by networkctl.

Start the new interface (or reboot):

sudo ifup enp3s0

And check if it is listed now:

sudo ifconfig