Score:0

iPerf3 UDP TX/RX bytes mismatch but no loss

pr flag

I am not able to interpret the following iPerf3 results.

Client:

iperf3 -c SERVER -u -R -b 350M

Connecting to host SERVER, port 5201
Reverse mode, remote host SERVER is sending
[  5] local CLIENT port 47128 connected to SERVER port 5201
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-1.00   sec  37.2 MBytes   312 Mbits/sec  0.039 ms  0/26961 (0%)  
[  5]   1.00-2.00   sec  37.0 MBytes   310 Mbits/sec  0.061 ms  0/26782 (0%)  
[  5]   2.00-3.00   sec  33.6 MBytes   281 Mbits/sec  0.047 ms  0/24297 (0%)  
[  5]   3.00-4.00   sec  36.5 MBytes   306 Mbits/sec  0.036 ms  0/26396 (0%)  
[  5]   4.00-5.00   sec  37.1 MBytes   312 Mbits/sec  0.061 ms  0/26895 (0%)  
[  5]   5.00-6.00   sec  37.2 MBytes   312 Mbits/sec  0.037 ms  0/26909 (0%)  
[  5]   6.00-7.00   sec  37.2 MBytes   312 Mbits/sec  0.079 ms  0/26954 (0%)  
[  5]   7.00-8.00   sec  37.1 MBytes   311 Mbits/sec  0.048 ms  0/26844 (0%)  
[  5]   8.00-9.00   sec  37.2 MBytes   312 Mbits/sec  0.037 ms  0/26930 (0%)  
[  5]   9.00-10.00  sec  37.2 MBytes   312 Mbits/sec  0.045 ms  0/26938 (0%)  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.03  sec   419 MBytes   350 Mbits/sec  0.000 ms  0/303148 (0%)  sender
[SUM]  0.0-10.0 sec  5 datagrams received out-of-order
[  5]   0.00-10.00  sec   367 MBytes   308 Mbits/sec  0.045 ms  0/265906 (0%)  receiver

Server:

Accepted connection from CLIENT, port 40876
[  5] local SERVER port 5201 connected to CLIENT port 47128
[ ID] Interval           Transfer     Bitrate         Total Datagrams
[  5]   0.00-1.00   sec  41.7 MBytes   350 Mbits/sec  30197  
[  5]   1.00-2.00   sec  41.7 MBytes   350 Mbits/sec  30216  
[  5]   2.00-3.00   sec  41.7 MBytes   350 Mbits/sec  30212  
[  5]   3.00-4.00   sec  41.7 MBytes   350 Mbits/sec  30215  
[  5]   4.00-5.00   sec  41.7 MBytes   350 Mbits/sec  30212  
[  5]   5.00-6.00   sec  41.7 MBytes   350 Mbits/sec  30219  
[  5]   6.00-7.00   sec  41.7 MBytes   350 Mbits/sec  30201  
[  5]   7.00-8.00   sec  41.7 MBytes   350 Mbits/sec  30230  
[  5]   8.00-9.00   sec  41.7 MBytes   350 Mbits/sec  30221  
[  5]   9.00-10.00  sec  41.7 MBytes   350 Mbits/sec  30194  
[  5]  10.00-10.03  sec  1.42 MBytes   351 Mbits/sec  1031  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.03  sec   419 MBytes   350 Mbits/sec  0.000 ms  0/303148 (0%)  sender

iPerf3 version on both server and client:

iperf 3.11 (cJSON 1.7.13)

The client has 300Mbit downstream connection to the internet, the server is hosted in a data center.

As the target bandwidth was set to 350M (which is greater than the bandwidth available for the client) I expected dropped packets. Surprisingly, iPerf reports 0% packet loss.

[  5]   0.00-10.03  sec   419 MBytes   350 Mbits/sec  0.000 ms  0/303148 (0%)  sender
[  5]   0.00-10.00  sec   367 MBytes   308 Mbits/sec  0.045 ms  0/265906 (0%)  receiver

Also the amount of data sent / received (419MB / 367MB) differ.

In addition, there is this last interval on the server side which I can not explain.

[  5]  10.00-10.03  sec  1.42 MBytes   351 Mbits/sec  1031  

Apparently, my knowledge is insufficient to explain this behavior. Hoping that someone can give me some insight.

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mangohost

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