Wed Mar 30, 2011 10:36 pm
Cacti is one solution, it graphs things for you via SNMP. There's also Nagios, which is an entire monitoring solutions. There are many other for pay and open source products. Mikrotik makes "The Dude", which is free.
Yes, one monitoring system instance would be able to monitor any system it can reach. And if you need to monitor systems you cannot reach via the public Internet you could always build VPN tunnels, and monitor across those.
An entirely different approach is Traffic Flow, which is a NetFlow implementation that returns on data connections through a router, including how many bytes were used in the connection, and which end points were involved. Again, there are many open source and for pay collectors out there. It is very commonly used for billing.
Getting a monitoring solution in place is a good idea for many reasons - not only will it persist storage of billing data for you, but it will also enable you to receive alerts when gear goes down, or passes critical thresholds for WAN circuit, memory, CPU etc. utilization.