Please set the following parameters in configuration file /etc/dpi/fastdpi.conf. You can find more details in option's description "Statistics collection and analysis":
netflow=3 netflow_dev=eth1 netflow_timeout=60 netflow_as_direction=3 netflow_collector=192.168.0.1:9997 netflow_as_collector=192.168.0.1:9998 #Turn on UDP detection only_tcp=0
Here:
192.168.0.1 - is IP address of a computer with nfsen
eth1 - is the network interface name to export netflow through. (Typically it is the same interface as the control one. DNA interfaces can not be used.)
only_tcp=0 - to switch on UDP protocols detection.