Checking bandwidth usage in realtime
You'll need bwm-ng for this, it's a really good utility to check BW usage, and even storage BW usage in realtime, for Debian based distros the installation as well is very simple:
apt-get install bwm-ng -y
Then, just start it:
On some network setups you need to increase the interval to get meaningfull, consistend data, you can change interval using the +/- keys, increase it to 1sec for most 1Gbps nodes.