After Ubuntu 12.04 the /etc/init.d/networking restart command will not work. So it is advised to create a restart script to be able to restart the network interface.
here are the steps done in creating the network restart script.
# vim nrestart.sh
This will create a new file. Then insert the following
ifdown eth0 && ifup eth0
Save after. Note replace the interface to suit your needs.
# chmod a+x nrestart.sh
This will make our script executable
# ./nrestart.sh
This is how to execute the command if you are in the same path.
