15

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?

Hao
  • 615

4 Answers4

29

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
J.P. Tosoni
  • 696
11

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
Community
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Dabu
  • 359
  • 1
  • 5
  • 23
0

You can use the -C command line option to force both ends to use an older version of the protocol and this will prevent the error.

From the help output:

-C, --compatibility      for use with older versions does not sent extra msgs
hardillb
  • 1,809
-1

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

service firewall off

to disable the firewall.

Shannon Nelson
  • 289