This bug is about the removal of NetworkManager's pre-up scripts functionality.
The pre-up script inside /etc/network/interfaces file still works. The problem is that if you configure an interface in the interfaces file, NM won't manage that interface. So, as NM ignores loopback, I put a loopback pre-up script in /etc/network/interfaces to do whatever I want before NM takes control of my eth.
@JoeDuncan
This bug is about the removal of NetworkManager's pre-up scripts functionality.
The pre-up script inside /etc/network/ interfaces file still works. The problem is that if you configure an interface in the interfaces file, NM won't manage that interface. So, as NM ignores loopback, I put a loopback pre-up script in /etc/network/ interfaces to do whatever I want before NM takes control of my eth.