I was talking to a bunch of people who run ISPs and other networks in
LDCs (yes, including Nigeria) and someone asked about monitoring tools
to watch traffic on his network so he can get advance warning of dodgy
customers and prevent complaints and blacklisting.
These people are plenty smart, but don't have a lot of money.
I'd say it's on topic. OpenNMS has good community support, as well as
reasonably priced commercial support - http://www.opennms.org/
I've used OpenNMS for years and it keeps getting better.
Enable NetFlow, and use some open-source NetFlow collection/analysis system like nfdump/nfsen, etc.
dnstop and the like for DNS can be pretty revealing, as well.
Coworkers of mine introduced me to Observium:
Does it utilize flow telemetry? On the main page, they talk about SNMP, making it sound a lot like Nagios . . .
No all stats are snmp based
Have them check out the various services from Team Cymru:
Specifically the TC Console