Licenses for commercial products are bound to the hardware where the software runs. Reinstalling the server where you run the commercial ntop products does not require a new license unless you change hardware. Products that use per-MAC licenses such as PF_RING ZC will work after reinstall if run on the same network interface, and per-system licenses (e.g. nProbe) will work too. In the latter case be aware that the license is based on the systemId that is computed using the CPU model and the MAC address of the management interface. This means that if you change the management interface while not changing anything else, the systemId will change and thus the license.