iperf connect failed: Connection refused

Question

iperf -c 192.168.3.2 -i 2 connect failed: Connection refused

3.2 is another machine. I think the port might be blocked.

How can I make this work?

This may be a stupid question, but: are you running "iperf -s" on 192.168.3.2? — Handyman5, Jun 16 '11 at 08:52
Another reason to get this error is running the IPerf server in UDP mode and client in TCP mode and vice versa. — user1407196, Jan 24 '13 at 14:46
Make sure Server & Client versions are the same... I had the same problem! — , Jul 26 '15 at 21:28

score 23 · Answer 1 · answered Apr 04 '16 at 10:46

23

You also get a "connection refused" error when you use an iperf v3 client to send to an iperf v2 server.

The message is slightly different though:

iperf3: error - unable to connect to server: Connection refused

As the iperf3 doc states, they are not compatible (at least up to version 3.1.2). You can check the version on both server and client with

iperf -v

answered Apr 04 '16 at 10:46

J.P. Tosoni

485
4
6

2

This is what happened to me. The windows version had the newest one (3.1.3) while for arch installing iperf gave me an old 2.0.5. Installing iperf3 on arch gave me the newest version, after which all went well. – hak8or Aug 14 '16 at 19:49
Even in 2022 this is so much useful ! Thanks – Vijay Gharge Sep 21 '22 at 04:45

score 11 · Answer 2 · edited Jan 21 '15 at 10:07

I doubt that this is a firewall issue. Usually, firewalls employ the DROP rule for packets that are not allowed. A "connection refused" means that there is no application listening on the port it tries to connect to. The destination host indicates this with a corresponding ICMP message to the source.

In order to run iperf you must have a server running on the machine which you iperf to. To do this run iperf -s on the server. After that you can then run iperf -c <server IP or hostname> -i 2

After running this you will get an ouput that looks something like this:

------------------------------------------------------------
Client connecting to <server IP>, TCP port 5000
TCP window size:   256 KByte (default)
------------------------------------------------------------
[  3] local 123.123.123.123 port 4000 connected with 123.123.123.123 port 5000
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.1 GBytes  1.09 Gbits/sec

score -1 · Answer 3 · answered Jun 16 '11 at 07:30

-1

Try turning off any firewall on the machines. On many linux distros, you can do

service firewall off

to disable the firewall.

answered Jun 16 '11 at 07:30

Shannon Nelson

279
2
8

iperf connect failed: Connection refused

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