SDN recently doing experiment, using a Floodlight + mininet, achieve the packet loss rate acquisition module, is thought by getting OFPortStatsReply, source sends packets and destination switch receives packets, packet loss ratio=(source send packets - purpose switch receives packets)/source switch to send packets; During the test, using mininet, build fattree topology, each link packet loss rate are 10% packet loss rate, however, the output is the source purpose of sending packets is equal to the switch receives packets, the packet loss rate is zero!!!!!! However the host is packet loss when ping each other!!!!!! Why is this? ! How to solve? ! For bosses to solve!