Network suddenly stopped working

[Michael Lange <klappnase@freenet.de>]

Hi,

since yesterday the network on my buster system all of a sudden refuses
to work. I am using systemd, no network-manager is running.
The /etc/network/interfaces file looks (as it did before) like:

auto lo
iface lo inet loopback

allow-hotplug enp2s0
iface enp2s0 inet dhcp

With ifconfig the enp2s0 interface appears to be up, the line that should
look similar to

        inet 192.168.178.33  netmask 255.255.255.0  broadcast 192.168.178.255

misses, though.
Trying `ifdown enp2s0` the command seems to never return.

I suspected udev to have for some reason changed the interface name; some
sources I found suggest to look at /etc/udev/rules.d/70-persistent-net.rules
but there is nothing in that file that is not commented out, so I guess
that this mechanism may be outdated.

The output of `systemctl status networking.service` looks like this:

● networking.service - Raise network interfaces
   Loaded: loaded (/lib/systemd/system/networking.service; enabled; vendor preset: enabled)
   Active: active (exited) since Mon 2021-07-12 10:40:20 CEST; 1h 27min ago
     Docs: man:interfaces(5)
  Process: 7545 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=0/SUCCESS)
 Main PID: 7545 (code=exited, status=0/SUCCESS)

Jul 12 10:40:19 miniac systemd[1]: Starting Raise network interfaces...
Jul 12 10:40:20 miniac systemd[1]: Started Raise network interfaces.

I a not sure what to make of all this, does anyone have a clue what else I
might try?

Thanks in advance

Michael