Comment 1 for bug 1301015

St├ęphane Graber (stgraber) wrote :

This was never a supported way to bounce the network, starting with 14.04, we changed the init script to fail rather than possibly trash your machine.

If you look at upstart's log, you'll notice the following message:
Stopping or restarting the networking job is not supported.
Use ifdown & ifup to reconfigure desired interface.