iperf3: error - control socket has closed unexpectedly (iperf 3.17.1 ) on Debian 12.7

[HenrikWahsner]

• Version of iperf3: Server: iperf 3.17.1 (cJSON 1.7.15) Client: iperf 3.17.1 (cJSON 1.7.15)

• Hardware: Server: ARMv7 VM Running Debian Client VM AMD64

• Operating system (and distribution, if any): Server: Debian 12.7 Client: Debian 12.7

Bug Report

Client 15.137.211.151 Server 15.137.211.152

Both systems are connected via LAN on the same switch.

When I run the test for the first time, I get an error message:

root@gj-inst-w10-amd64:~# iperf3 --client 15.137.211.152 --get-server-output --bitrate 1M --interval 1 --time 10 --len 0 --parallel 4 --bidir
Connecting to host 15.137.211.152, port 5201
[  5] local 15.137.211.151 port 45090 connected to 15.137.211.152 port 5201
[  7] local 15.137.211.151 port 45100 connected to 15.137.211.152 port 5201
[  9] local 15.137.211.151 port 45116 connected to 15.137.211.152 port 5201
[ 11] local 15.137.211.151 port 45128 connected to 15.137.211.152 port 5201
[ 13] local 15.137.211.151 port 45144 connected to 15.137.211.152 port 5201
[ 15] local 15.137.211.151 port 45148 connected to 15.137.211.152 port 5201
[ 17] local 15.137.211.151 port 45164 connected to 15.137.211.152 port 5201
[ 19] local 15.137.211.151 port 45172 connected to 15.137.211.152 port 5201
iperf3: error - control socket has closed unexpectedly
root@gj-inst-w10-amd64:~#

If I run it right after again, all is working fine, here the last lines:

[ 13][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec    0             sender
[ 13][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec                  receiver
[ 15][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec    0             sender
[ 15][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec                  receiver
[ 17][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec    0             sender
[ 17][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec                  receiver
[ 19][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec    0             sender
[ 19][RX-C]   0.00-10.00  sec  1.25 MBytes  1.05 Mbits/sec                  receiver
[SUM][RX-C]   0.00-10.00  sec  5.00 MBytes  4.19 Mbits/sec    0             sender
[SUM][RX-C]   0.00-10.00  sec  5.00 MBytes  4.19 Mbits/sec                  receiver

iperf Done.

I have attached a trace of the server side. In the first failing test one side is resetting in the middle of the connection.

I can reproduce it every time. If there is more time between 2 tests ( more than around 3 minutes) then the first test is failing again. If I run many test after the previous test ended all is fine, if there is less time between tests

iperf.zip

EDIT: I found out, that this only happens with option --bidir If I don't use this option, the test is Running as expected.