I'm using Ubuntu on VirtualBox, but I think this is not important in my case.

When I use the command
Code:
sudo ifconfig eth1 192.168.2.1 netmask 255.255.255.0 broadcast 192.168.2.255 up
the interface works as expected, in fact I can ping other (virtual) machines on the same subnet.

But after a while (even if I don't perform any action) seems like the interface "loses" its ipv4 configuration, in fact the output of
Code:
ifconfig
is


As you can see, the line of the ipv4 configuration is absent.

Why? How can I resolve?