Iperf3 client reporting zero data even though the server is receiving traffic

[yennym3]

Hi, I'm trying to do some throughput measurements, I sometimes get 0.00 on the Transfer and Bitrate fields like the following

On the server side I run the following command iperf3 -s

On the client side I run the following command: iperf3 -c 10.0.12.1 -t 30

On the client side:

Is is what I receive on the server:

When I set the TCP -w 64k window, there is no transfer 0.0.0, but if I try to extend it to w -128k, it appears again iperf3 -c 10.0.12.1 -t 30 -w 64k Is is what I receive on the server:

If I decrease the packet size -l 1k , or -l 10k this also happens iperf3 -c 10.0.12.1 -t 30 -l 1k

Can anyone help me locate where the problem is? Before reducing the window, I would like to enlarge it, but 0 transfers are displayed, using UDP this does not happen.

[davidBar-On]

Can anyone help me locate where the problem is?

I don't have an answer, but some points that can help evaluation:

1. From the -w 64k test, the link throughput is about 115KB/sec, which probably means that there is a 1Mbits/sec limit between the client and server. Do you know what is the reason for this throughput limit?
2. When running UDP test, what is the maximum throughput on the server side? Note that the default UDP sending rate is 1Mbits/sec (128KB/sec). Use -b to set the sending rate.
3. Are the client and server connected directly, or are there other components (switch, router, etc.) between them? It may be that the problem is related to such component and its settings.
4. Run the client and server with the --debug=3 option. What is reported as "SNDBUF is ..." and "SNDBUF is ..."? May help to understand the buffer sizes used.
5. See this explanation about Scaling TCP Window size and related OS settings. Note that per this explanation, increasing the windows size for slow networks may be a problem: "TCP window scaling will actually cause more problems than it solves, especially when the network is unreliable or slow".