====== netflow ======

  * ntopng
    * needs ''nProbe'' (non free) to receive NetFlow 
    * free ''netflow2ng'' exists
  * Akvorado
    * free (AGPL3)
    * high demands (ClickHouse time-series database)
  * ELK Stack
  * ElastiFlow
    * possible to obtain free Basic License:
      * no usage limits - commercial companies also
      * capacity limit - 4000 flow records per second
      * device limit - 25 devices for SNMP polling and trap