If you have a server transmissiting or recieving lots of data then you can use the following tools to investigate:
First run:

sar -n DEV

This will show you the history of networking.

sar -n DEV -s `date -d '-3 hour' +%T` |awk '{if ($3 == "IFACE" || $3 == "eth0" || $2 == "eth0") {print}}'

You can then use the following tools to get an understanding of which service is using the most networking traffic and what IP address it is coming from or going to:

yum install nethogs

Then run:

nethogs

Currently trying to figure out how to copy and paste from it