There are various freely available Unix flavors out there.
The most popular ones are Linux (which is Unix-system, yes)
with its different distributions (the most popular here are
Debian under http://www.debian.org/
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg).
If you're looking for how to monitor bandwidth using netflow or packet s…