Network interface does not show up with ifconfig and Internet does not work

If for some reasons your ethernet network interface does not show up with ifconfig command, you can do the following to find it and raise it up again:

1. Find the interface:

ifconfig -a

enp0s31f6 ... DOWN

2. Up the missing interface:

sudo ifconfig enp0s31f6 up

3. Call the DHCP client on the missing interface:

sudo dhclient enp0s31f6

After that, you will be able to access the Internet again.