You can use tcpdump tool. Run the following command:

tcpdump –n udp

or

tcpdump –n udp and port 2000

 

You will see all UDP packets that the netflow server receives. You can break tcpdump by typing <Ctrl>+C. If you don’t see any packet, check network cable and/or netflow configuration on Cisco router and try debugging netflow exports. If you see incoming packets, but netflow collector still don’t receive any packet check your Status->Collector->Detail menu, firewall configuration and system log file (syslog). Port 2000 is used as example.