Nagios Support Forum

OK.
Make sure the WS-C3850-48XS is setup to send the Netflow data like the example in the following guide and see if that fixes the issue.
https://assets.nagios.com/downloads/nag ... alyzer.pdf

Thank you but it appears that the configuration is already correct.
Moreover I have other devices of the same model, and they send data wich is properly collected by the network analyzer.

I don't know what else to say. The data captured with tcpdump does not show any valid data so it has to either be a configuration problem or a bug in the Cisco IOS.
Make sure the everything is up to date on the Switch.