Cacti is one of the most powerful open source front ends for RRDtool. Jack Wallen walks you through the steps to get this up and running, so you can gain access to handy network and system graphics.
SNMP v3 is more like a user/password setup and is good to do if you can easily set it up on the devices and PRTG server. The switches and firewall will (at least the firewall for sure) require that ...