iperf Iperf3 client reporting zero data even even though server receives traffic

Version of iperf3: 3.11
Hardware: x86-64
Operating system (and distribution, if any): Ubuntu-20.04.1

Bug Report

Expected Behavior

Transfer and Bitrate should not be show 0
Actual Behavior

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 **** Issue [ 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 **** Issue [ 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 **** Issue [ 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 **** Issue
[ 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 **** Issue
[ 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.

I also run the above client command with --debug and --verbose and I got the following:

user@user-VirtualBox:~$ iperf3 -c xxxxxxxxxxxxxx -p xxxxx -t5 -i 0.5 --verbose --debug iperf 3.11 Linux user-VirtualBox 5.13.0-28-generic #31~20.04.1-Ubuntu SMP Wed Jan 19 14:08:10 UTC 2022 x86_64 Control connection MSS 1460 send_parameters: { "tcp": true, "omit": 0, "time": 5, "parallel": 1, "len": 131072, "pacing_timer": 1000, "client_version": "3.11" } Time: Tue, 05 Apr 2022 10:44:51 GMT Connecting to host xxxxxxxxxxxxxx, port xxxxx Cookie: swus4psvwnbb6vlwnpgbxxlpg6fwaeixybeg TCP MSS: 1460 (default) SNDBUF is 16384, expecting 0 RCVBUF is 131072, expecting 0 Congestion algorithm is cubic [ 5] local 10.0.2.15 port 53426 connected to 51.144.127.180 port xxxxx Starting Test: protocol: TCP, 1 streams, 131072 byte blocks, omitting 0 seconds, 5 second test, tos 0 sent 108040 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 0 bytes of 131072, pending 23032, total 108040 sent 23032 bytes of 131072, pending 0, total 131072 sent 41208 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 0 bytes of 131072, pending 89864, total 172280 sent 64240 bytes of 131072, pending 25624, total 236520 sent 25624 bytes of 131072, pending 0, total 262144 sent 6496 bytes of 131072, pending 124576, total 268640 sent 0 bytes of 131072, pending 124576, total 268640 sent 0 bytes of 131072, pending 124576, total 268640 sent 0 bytes of 131072, pending 124576, total 268640 sent 0 bytes of 131072, pending 124576, total 268640 sent 0 bytes of 131072, pending 124576, total 268640 sent 32120 bytes of 131072, pending 92456, total 300760 sent 0 bytes of 131072, pending 92456, total 300760 sent 92456 bytes of 131072, pending 0, total 393216 sent 3904 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 0 bytes of 131072, pending 127168, total 397120 sent 127168 bytes of 131072, pending 0, total 524288 sent 1312 bytes of 131072, pending 129760, total 525600 sent 32120 bytes of 131072, pending 97640, total 557720 sent 0 bytes of 131072, pending 97640, total 557720 sent 0 bytes of 131072, pending 97640, total 557720 sent 0 bytes of 131072, pending 97640, total 557720 sent 0 bytes of 131072, pending 97640, total 557720 sent 0 bytes of 131072, pending 97640, total 557720 sent 0 bytes of 131072, pending 97640, total 557720 sent 0 bytes of 131072, pending 97640, total 557720 tcpi_snd_cwnd 25 tcpi_snd_mss 1460 tcpi_rtt 254 interval_len 0.506785 bytes_transferred 557720 interval forces keep [ ID] Interval Transfer Bitrate Retr Cwnd [ 5] 0.00-0.51 sec 545 KBytes 8.80 Mbits/sec 0 35.6 KBytes
sent 96360 bytes of 131072, pending 1280, total 654080 sent 0 bytes of 131072, pending 1280, total 654080 sent 0 bytes of 131072, pending 1280, total 654080 sent 0 bytes of 131072, pending 1280, total 654080 sent 1280 bytes of 131072, pending 0, total 655360 sent 30840 bytes of 131072, pending 100232, total 686200 sent 0 bytes of 131072, pending 100232, total 686200 sent 0 bytes of 131072, pending 100232, total 686200 sent 0 bytes of 131072, pending 100232, total 686200 sent 0 bytes of 131072, pending 100232, total 686200 sent 100232 bytes of 131072, pending 0, total 786432 sent 28248 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 sent 0 bytes of 131072, pending 102824, total 814680 tcpi_snd_cwnd 34 tcpi_snd_mss 1460 tcpi_rtt 290 interval_len 0.577949 bytes_transferred 256960 interval forces keep [ 5] 0.51-1.08 sec 251 KBytes 3.56 Mbits/sec 0 48.5 KBytes
sent 102824 bytes of 131072, pending 0, total 917504 sent 25656 bytes of 131072, pending 105416, total 943160 sent 32120 bytes of 131072, pending 73296, total 975280 sent 0 bytes of 131072, pending 73296, total 975280 sent 0 bytes of 131072, pending 73296, total 975280 sent 0 bytes of 131072, pending 73296, total 975280 sent 0 bytes of 131072, pending 73296, total 975280 sent 0 bytes of 131072, pending 73296, total 975280 sent 0 bytes of 131072, pending 73296, total 975280 sent 0 bytes of 131072, pending 73296, total 975280 sent 73296 bytes of 131072, pending 0, total 1048576 sent 119424 bytes of 131072, pending 11648, total 1168000 sent 0 bytes of 131072, pending 11648, total 1168000 sent 0 bytes of 131072, pending 11648, total 1168000 sent 0 bytes of 131072, pending 11648, total 1168000 sent 0 bytes of 131072, pending 11648, total 1168000 sent 0 bytes of 131072, pending 11648, total 1168000 sent 0 bytes of 131072, pending 11648, total 1168000 sent 11648 bytes of 131072, pending 0, total 1179648 sent 20472 bytes of 131072, pending 110600, total 1200120 sent 110600 bytes of 131072, pending 0, total 1310720 sent 82120 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 sent 0 bytes of 131072, pending 48952, total 1392840 tcpi_snd_cwnd 46 tcpi_snd_mss 1460 tcpi_rtt 851 interval_len 0.416079 bytes_transferred 578160 interval forces keep [ 5] 1.08-1.50 sec 565 KBytes 11.1 Mbits/sec 0 65.6 KBytes
tcpi_snd_cwnd 46 tcpi_snd_mss 1460 tcpi_rtt 649 interval_len 0.520614 bytes_transferred 0 interval forces keep [ 5] 1.50-2.02 sec 0.00 Bytes 0.00 bits/sec 0 65.6 KBytes **** Issue
sent 48952 bytes of 131072, pending 0, total 1441792 sent 131072 bytes of 131072, pending 0, total 1572864 sent 12696 bytes of 131072, pending 118376, total 1585560 sent 0 bytes of 131072, pending 118376, total 1585560 sent 0 bytes of 131072, pending 118376, total 1585560 sent 0 bytes of 131072, pending 118376, total 1585560 sent 0 bytes of 131072, pending 118376, total 1585560 sent 0 bytes of 131072, pending 118376, total 1585560 sent 0 bytes of 131072, pending 118376, total 1585560 sent 0 bytes of 131072, pending 118376, total 1585560 sent 118376 bytes of 131072, pending 0, total 1703936 sent 42224 bytes of 131072, pending 88848, total 1746160 sent 0 bytes of 131072, pending 88848, total 1746160 sent 0 bytes of 131072, pending 88848, total 1746160 sent 0 bytes of 131072, pending 88848, total 1746160 sent 0 bytes of 131072, pending 88848, total 1746160 sent 0 bytes of 131072, pending 88848, total 1746160 sent 0 bytes of 131072, pending 88848, total 1746160 sent 0 bytes of 131072, pending 88848, total 1746160 sent 32120 bytes of 131072, pending 56728, total 1778280 sent 56728 bytes of 131072, pending 0, total 1835008 sent 131072 bytes of 131072, pending 0, total 1966080 sent 4920 bytes of 131072, pending 126152, total 1971000 sent 0 bytes of 131072, pending 126152, total 1971000 sent 0 bytes of 131072, pending 126152, total 1971000 sent 0 bytes of 131072, pending 126152, total 1971000 sent 0 bytes of 131072, pending 126152, total 1971000 sent 0 bytes of 131072, pending 126152, total 1971000 sent 0 bytes of 131072, pending 126152, total 1971000 sent 0 bytes of 131072, pending 126152, total 1971000 tcpi_snd_cwnd 47 tcpi_snd_mss 1460 tcpi_rtt 639 interval_len 0.479286 bytes_transferred 578160 interval forces keep [ 5] 2.02-2.50 sec 565 KBytes 9.65 Mbits/sec 0 67.0 KBytes
sent 126152 bytes of 131072, pending 0, total 2097152 sent 34448 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 sent 0 bytes of 131072, pending 96624, total 2131600 tcpi_snd_cwnd 47 tcpi_snd_mss 1460 tcpi_rtt 751 interval_len 0.500693 bytes_transferred 160600 interval forces keep [ 5] 2.50-3.00 sec 157 KBytes 2.57 Mbits/sec 0 67.0 KBytes
sent 96624 bytes of 131072, pending 0, total 2228224 sent 96096 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 0 bytes of 131072, pending 34976, total 2324320 sent 34976 bytes of 131072, pending 0, total 2359296 sent 131072 bytes of 131072, pending 0, total 2490368 sent 26672 bytes of 131072, pending 104400, total 2517040 sent 0 bytes of 131072, pending 104400, total 2517040 sent 0 bytes of 131072, pending 104400, total 2517040 sent 0 bytes of 131072, pending 104400, total 2517040 sent 0 bytes of 131072, pending 104400, total 2517040 sent 0 bytes of 131072, pending 104400, total 2517040 sent 0 bytes of 131072, pending 104400, total 2517040 sent 0 bytes of 131072, pending 104400, total 2517040 tcpi_snd_cwnd 47 tcpi_snd_mss 1460 tcpi_rtt 622 interval_len 0.498952 bytes_transferred 385440 interval forces keep [ 5] 3.00-3.50 sec 376 KBytes 6.18 Mbits/sec 0 67.0 KBytes
sent 104400 bytes of 131072, pending 0, total 2621440 sent 88320 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 0 bytes of 131072, pending 42752, total 2709760 sent 42752 bytes of 131072, pending 0, total 2752512 sent 131072 bytes of 131072, pending 0, total 2883584 sent 18896 bytes of 131072, pending 112176, total 2902480 sent 0 bytes of 131072, pending 112176, total 2902480 sent 0 bytes of 131072, pending 112176, total 2902480 sent 0 bytes of 131072, pending 112176, total 2902480 sent 0 bytes of 131072, pending 112176, total 2902480 sent 0 bytes of 131072, pending 112176, total 2902480 sent 0 bytes of 131072, pending 112176, total 2902480 sent 0 bytes of 131072, pending 112176, total 2902480 tcpi_snd_cwnd 47 tcpi_snd_mss 1460 tcpi_rtt 579 interval_len 0.499736 bytes_transferred 385440 interval forces keep [ 5] 3.50-4.00 sec 376 KBytes 6.17 Mbits/sec 0 67.0 KBytes
sent 112176 bytes of 131072, pending 0, total 3014656 sent 48424 bytes of 131072, pending 82648, total 3063080 sent 32120 bytes of 131072, pending 50528, total 3095200 sent 0 bytes of 131072, pending 50528, total 3095200 sent 0 bytes of 131072, pending 50528, total 3095200 sent 0 bytes of 131072, pending 50528, total 3095200 sent 0 bytes of 131072, pending 50528, total 3095200 sent 0 bytes of 131072, pending 50528, total 3095200 sent 0 bytes of 131072, pending 50528, total 3095200 sent 0 bytes of 131072, pending 50528, total 3095200 tcpi_snd_cwnd 47 tcpi_snd_mss 1460 tcpi_rtt 567 interval_len 0.500108 bytes_transferred 192720 interval forces keep [ 5] 4.00-4.50 sec 188 KBytes 3.08 Mbits/sec 0 67.0 KBytes
sent 50528 bytes of 131072, pending 0, total 3145728 sent 131072 bytes of 131072, pending 0, total 3276800 sent 11120 bytes of 131072, pending 119952, total 3287920 sent 0 bytes of 131072, pending 119952, total 3287920 sent 0 bytes of 131072, pending 119952, total 3287920 sent 0 bytes of 131072, pending 119952, total 3287920 sent 0 bytes of 131072, pending 119952, total 3287920 sent 0 bytes of 131072, pending 119952, total 3287920 sent 0 bytes of 131072, pending 119952, total 3287920 sent 0 bytes of 131072, pending 119952, total 3287920 sent 119952 bytes of 131072, pending 0, total 3407872 sent 40648 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 sent 0 bytes of 131072, pending 90424, total 3448520 tcpi_snd_cwnd 47 tcpi_snd_mss 1460 tcpi_rtt 756 send_results { "cpu_util_total": 3.1065353728139713, "cpu_util_user": 0.72940041220517571, "cpu_util_system": 2.3771349606087955, "sender_has_retransmits": 1, "congestion_used": "cubic", "streams": [{ "id": 1, "bytes": 3448520, "retransmits": 0, "jitter": 0, "errors": 0, "packets": 0, "start_time": 0, "end_time": 5.000356 }] } get_results { "cpu_util_total": 0.050793, "cpu_util_user": 0.01956, "cpu_util_system": 0.031233, "sender_has_retransmits": -1, "streams": [{ "id": 1, "bytes": 2882353, "retransmits": -1, "jitter": 0, "errors": 0, "packets": 0 }] } interval_len 0.500154 bytes_transferred 353320 interval forces keep [ 5] 4.50-5.00 sec 345 KBytes 5.65 Mbits/sec 0 67.0 KBytes

Test Complete. Summary Results: [ ID] Interval Transfer Bitrate Retr [ 5] 0.00-5.00 sec 3.29 MBytes 5.52 Mbits/sec 0 sender [ 5] 0.00-5.00 sec 2.75 MBytes 4.61 Mbits/sec receiver CPU Utilization: local/sender 3.1% (0.7%u/2.4%s), remote/receiver 0.1% (0.0%u/0.0%s) snd_tcp_congestion cubic

iperf Done.

You can check the zero value lines by searching **** Issue.

What do you think is wring here?

Apr 05 '22 12:04 dk1301

What happens if you use a 1 second interval?

Apr 06 '22 13:04 TheRealDJ

The issue is probably because iperf3 default TCP block length sent is 128K (the "131072 byte blocks") and the about 300-400KB/sec (150-200KB/0.5 sec) throughput. The client quickly fills the TCP buffer - the about 700KB the client reported at the first 0.5 sec interval. Therefore, in different 0.5 sec intervals the client's TCP buffer is full not no data is sent. If this is the reason, then using smaller blocks, e.g. -l 10K, will solve the problem.

Apr 07 '22 05:04 davidBar-On

Hi again after doing several tests I noticed the following :

With interval 1 s the 0 case never happens
By changing the buffer size from the default TCP 128k to 10k it happens but not as frequent as the 128k one. Specifically for a 128k measurement one may see more than one 0 values while with the 10k maximum 1.
The same as 2 happens whether using 20k, 30k etc.
The 0 case never happens when the -R (download) parameter is used.

Since I need the interval to be less than 1 s can you suggest anything else or is this an iperf limitation I need to live with ?

Apr 07 '22 11:04 dk1301

Hi,

.... 0 values while with the 10k maximum 1.

Is this one 0 in the second interval (0.5 - 1 sec)? If it is, then the problem is probably related to the initiation of the connection which takes relatively long time, so the amount of data transferred in the first 0.5 sec. is small. If this is the problem, you can omit the first 2 seconds of the test adding --omit 2. The test will run for 7 secs (2+5) and the first 2 secs statistics will be ignored.

Another option may be to further reduce the block size, e.g. -l 1K.

Apr 07 '22 19:04 davidBar-On