I'm trying to do some throughput measurements for a azure VM ubuntu server using iperf3.(version iperf 3.11).
In the server side I run the following command
iperf3 -s -V -p xxxx
On the client side when I give the following command for 5 second test and 0.5 seconds report interval
iperf3 -c hostname -p xxxx -t 5 -i 0.5
I sometimes get 0.0 on the Transfer and Bitrate fields like the following
Connecting to host xxxxxxxxx, port xxxx
[ 5] local 10.0.2.15 port 36280 connected to xxxxxxxxx port xxxxxxx
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-0.50 sec 656 KBytes 10.7 Mbits/sec 0 65.6 KBytes
[ 5] 0.50-1.01 sec 0.00 Bytes 0.00 bits/sec 0 65.6 KBytes
[ 5] 1.01-1.52 sec 188 KBytes 3.04 Mbits/sec 0 65.6 KBytes
[ 5] 1.52-2.00 sec 188 KBytes 3.18 Mbits/sec 0 65.6 KBytes
[ 5] 2.00-2.50 sec 0.00 Bytes 0.00 bits/sec 0 65.6 KBytes
[ 5] 2.50-3.00 sec 157 KBytes 2.57 Mbits/sec 0 62.7 KBytes
[ 5] 3.00-3.50 sec 314 KBytes 5.14 Mbits/sec 0 65.6 KBytes
[ 5] 3.50-4.00 sec 188 KBytes 3.09 Mbits/sec 0 65.6 KBytes
[ 5] 4.00-4.52 sec 188 KBytes 2.98 Mbits/sec 0 65.6 KBytes
[ 5] 4.52-5.13 sec 188 KBytes 2.53 Mbits/sec 0 65.6 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-5.13 sec 2.02 MBytes 3.30 Mbits/sec 0 sender
[ 5] 0.00-5.13 sec 1.68 MBytes 2.74 Mbits/sec
Even though on the server side I get non zero values
[ 5] local 10.0.1.4 port yyyyyy connected to xxxxxxx port xxxxxxx
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-1.00 sec 199 KBytes 1.63 Mbits/sec
[ 5] 1.00-2.00 sec 315 KBytes 2.58 Mbits/sec
[ 5] 2.00-3.00 sec 302 KBytes 2.47 Mbits/sec
[ 5] 3.00-4.00 sec 417 KBytes 3.42 Mbits/sec
[ 5] 4.00-5.00 sec 391 KBytes 3.20 Mbits/sec
[ 5] 5.00-5.22 sec 93.9 KBytes 3.57 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-5.22 sec 0.00 Bytes 0.00 bits/sec sender
[ 5] 0.00-5.22 sec 1.68 MBytes 2.70 Mbits/sec receiver
----------------------------------------------------------
The above happens even if I start the server with the following command
iperf -s -V -p xxxx -i 0.5
Which means that there is no way for the uplink to be at that moment 0.
E.x
client side
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-0.50 sec 730 KBytes 11.9 Mbits/sec 0 92.7 KBytes
[ 5] 0.50-1.00 sec 0.00 Bytes 0.00 bits/sec 0 88.4 KBytes
[ 5] 1.00-1.51 sec 220 KBytes 3.52 Mbits/sec 0 88.4 KBytes
[ 5] 1.51-2.01 sec 0.00 Bytes 0.00 bits/sec 0 91.2 KBytes
[ 5] 2.01-2.52 sec 251 KBytes 4.06 Mbits/sec 0 91.2 KBytes
[ 5] 2.52-3.00 sec 220 KBytes 3.73 Mbits/sec 0 91.2 KBytes
[ 5] 3.00-3.50 sec 220 KBytes 3.59 Mbits/sec 0 91.2 KBytes
[ 5] 3.50-4.00 sec 220 KBytes 3.60 Mbits/sec 0 91.2 KBytes
[ 5] 4.00-4.50 sec 0.00 Bytes 0.00 bits/sec 0 91.2 KBytes
[ 5] 4.50-5.00 sec 188 KBytes 3.10 Mbits/sec 0 91.2 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-5.00 sec 2.00 MBytes 3.35 Mbits/sec 0 sender
[ 5] 0.00-5.00 sec 1.59 MBytes 2.66 Mbits/sec receiver
iperf Done.
server side
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-0.50 sec 63.3 KBytes 1.04 Mbits/sec
[ 5] 0.50-1.00 sec 101 KBytes 1.66 Mbits/sec
[ 5] 1.00-1.50 sec 116 KBytes 1.91 Mbits/sec
[ 5] 1.50-2.00 sec 145 KBytes 2.37 Mbits/sec
[ 5] 2.00-2.50 sec 194 KBytes 3.18 Mbits/sec
[ 5] 2.50-3.00 sec 194 KBytes 3.17 Mbits/sec
[ 5] 3.00-3.50 sec 197 KBytes 3.22 Mbits/sec
[ 5] 3.50-4.00 sec 201 KBytes 3.29 Mbits/sec
[ 5] 4.00-4.50 sec 199 KBytes 3.27 Mbits/sec
[ 5] 4.50-5.00 sec 199 KBytes 3.27 Mbits/sec
[ 5] 5.00-5.07 sec 14.3 KBytes 1.59 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-5.07 sec 0.00 Bytes 0.00 bits/sec sender
[ 5] 0.00-5.07 sec 1.59 MBytes 2.62 Mbits/sec receiver
The above does not happen when I use the default interval 1 sec and also when I use the -R parameter to measure download.
Can anyone help me to locate where the problem is ?
The problem is probably because iperf3 feels the network buffers fater then the transmit rate, so the buffers become full. For example, in the second test, the client sent 730KB in the first second, but the server received only 63KB.
Also, in both tests the client sent about 300-400KB more than the server received. This is the amount of data that was still in the network buffers when the client completed sending (in iperf3 the client is responsible to set the end of the test).
See the related discussion in iperf3 issue #1308.