How can iperf reporting packet loss in udp

Question

Iperf is the well known tool to calculate throughput. When i tried udp throughput using iperf on my linuxpc, It reported that 10% of packet loss.

In UDP protocol, data gram did not receice any acknowledgements. But, in what way iperf is reporting or calculating packet loss ? How would iperf tool know whether transmitted datagram received or not. I wonder about this.

Answer 1

iperf itself is including sequence numbers into its datagrams, which are not standard in UDP. Where there is a gap, it assumes loss. See iperf_udp.c

There exist Wireshark dissectors that will extract the numbers from a packet capture. iperf udp sequence number wireshark