Install NTop to monitor all the traffic of your machines in your network.

Step 1 :

sudo apt-get install ntop rrdtool

Step 2 :

Set the admin password.

sudo ntop -A

Step 3 :

sudo ntop -d -L

You can add to the /etc/rc.local to make it execute when boot up automatically.

Step 4 :

Access ntop at http://ip_address_ntop:3000

Enjoy!