Refer to GPT and yourself. Based on the information you provided, it looks like your Mininet network has been set up, but the iperf test did not succeed. Here are some possible causes and solutions:
1 Check whether the network topology is correctly configured. Ensure that h1 and h2 are on the same subnet, h3 and h4 are on another subnet, and switches are correctly connected.
2 Ensure that the IP addresses of h1 and h2 are correctly configured and can ping each other.
3 Make sure you have started the iperf server and client on h1 and h2. You can start the iperf server on h1 and the iperf client on h2.
4 Ensure that the firewall is turned off or configured correctly to allow iperf traffic through.
5 Try using different iperf options, such as -b and -t, to get a better idea of the problem. You can try specifying the bandwidth and duration on the command line, for example:
iperf -c h1 -t 10 -b 100M
6 If the above methods do not solve the problem, check Mininet's log file for more details. You can open the log file with the following command:
sudo mn --clean; sudo mn --loglevel debug > mininet.log 2>&1
Then look at the mininet.log file for more information.
Hope these methods can help you solve the problem.