If you’re going to deploy FastNetMon to really big network, you found best guide about it. You can find some basic numbers about required hardware in our install guide.
We have confirmed deployments for more than 400 Gbps of capacity in Netflow and sFlow modes. In Netflow/IPFIX or sFlow modes FastNetMon scales almost indefinitely. FastNetMon uses our own proprietary high optimised packet parser and it was tested with ~1.2Tbps of real traffic. Only one issue you can hit is memory usage for IPv4 counters, FastNetMon allocates them statically for each host, you can calculate memory requirements for your network using this formula. For IPv6 counters we use new dynamic counters and they allocate memory on demand.
In port mirror / SPAN mode FastNetMon can use all your available CPU resources. You will need 2-4 CPU cores for each 10-40G port. Also, you can use kernel side sampling introduced recently and it can lower hardware requirements to 1-2 CPU cores for 40G interface with decent network card.
For baseline calculation, FastNetMon uses only single thread (limited by single CPU core performance) and it may affect you in case of really big number of IPv4 hosts (hundreds of millions or more). If you experience delays or issues with it, please contacts our support team.