Monitor network traffic volume over interface
The data you want to see shows up in good old ifconfig.
watch ifconfig eth0
or to make things stand out better:
watch -n 1 -d ifconfig eth0
I use iftop command. It shows statistics in realtime.
iftop -i eth0
Checkout some sceenshots here:
http://www.thegeekstuff.com/2008/12/iftop-guide-display-network-interface-bandwidth-usage-on-linux/
on post-2015 or so linux this might be better
watch -n1 -d ip -s link show [interface]