Applications listed as '_app'

NetFlow Analyzer calculates traffic based on the port and protocol maps available. We have around 10000 applications mapped based on the IANA which you can find under Application/QoS mapping.  

If there is traffic in your network which uses ports / protocols that are not mapped under Application/QoS mapping database, it will be categorized as Unknown_ app. You can map this application using the "Show ports". Once this is done, it will be categorizes under the given name from the very next flow. Check the link below for more information on this.

https://forums.manageengine.com/topic/unknown-application-port-protocol

Port level information can be retrieved using raw data. Set the raw data retention period to 1 hour under Settings -> NetFlow -> Raw Data Settings, and check the last hour report. The unknown app details displayed can be used for configuration.