Using iperf on a Microsoft Windows system

Iperf is a free open-source software tool that provides a capability to measure the throughput between two hosts using both Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) data streams. The software can be run in either server or client mode. To determine the network bandwidth available between two systems, you can run iperf in server mode on one of the systems and in client mode on the other.

The software is available for a variety of operating systems. You can download iPerf binaries from iPerf - The network bandwidth measurement tool for the following operating systems:

  1. Microsoft Windows
  2. Android
  3. iPhone / iPad
  4. Apple OS X
  5. Download iPerf for Ubuntu / Debian / Mint
  6. Download iPerf for Fedora / Red Hat / CentOS
  7. Download iPerf for openSUSE
  8. Download iPerf for Arch Linux
  9. Download iPerf for FreeBSD

You can also download the C++ source code from that page. Alternatively, if you are using a Linux distribution, you may be able to install it using a standard package management tool for the particular distribution of Linux that you are using. E.g., see Installing iperf on CentOS for instructions on how to install the software with yum.

If you install the software on two systems you control, you can test between those systems. There are also public iPerf3 servers in various parts of the world with which you can test. Those systems are running in server mode, so you use client mode on your local system when testing with them. You specify client mode with the -c option. You can see the available options for the program by issuing the command iperf -h from a command prompt while in the directory where you installed the software on the Microsoft Windows system.

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Usage: iperf [-s|-c host] [options]
       iperf [-h|--help] [-v|--version]

Server or Client:
  -p, --port      #         server port to listen on/connect to
  -f, --format    [kmgKMG]  format to report: Kbits, Mbits, KBytes, MBytes
  -i, --interval  #         seconds between periodic bandwidth reports
  -F, --file name           xmit/recv the specified file
  -B, --bind      <host>    bind to a specific interface
  -V, --verbose             more detailed output
  -J, --json                output in JSON format
  --logfile f               send output to a log file
  -d, --debug               emit debugging output
  -v, --version             show version information and quit
  -h, --help                show this message and quit
Server specific:
  -s, --server              run in server mode
  -D, --daemon              run the server as a daemon
  -I, --pidfile file        write PID file
  -1, --one-off             handle one client connection then exit
Client specific:
  -c, --client    <host>    run in client mode, connecting to <host>
  -u, --udp                 use UDP rather than TCP
  -b, --bandwidth #[KMG][/#] target bandwidth in bits/sec (0 for unlimited)
                            (default 1 Mbit/sec for UDP, unlimited for TCP)
                            (optional slash and packet count for burst mode)
  -t, --time      #         time in seconds to transmit for (default 10 secs)
  -n, --bytes     #[KMG]    number of bytes to transmit (instead of -t)
  -k, --blockcount #[KMG]   number of blocks (packets) to transmit (instead of -
t or -n)
  -l, --len       #[KMG]    length of buffer to read or write
                            (default 128 KB for TCP, 8 KB for UDP)
  --cport         <port>    bind to a specific client port (TCP and UDP, default
: ephemeral port)
  -P, --parallel  #         number of parallel client streams to run
  -R, --reverse             run in reverse mode (server sends, client receives)
  -w, --window    #[KMG]    set window size / socket buffer size
  -M, --set-mss   #         set TCP/SCTP maximum segment size (MTU - 40 bytes)
  -N, --no-delay            set TCP/SCTP no delay, disabling Nagle's Algorithm
  -4, --version4            only use IPv4
  -6, --version6            only use IPv6
  -S, --tos N               set the IP 'type of service'
  -Z, --zerocopy            use a 'zero copy' method of sending data
  -O, --omit N              omit the first n seconds
  -T, --title str           prefix every output line with this string
  --get-server-output       get results from server
  --udp-counters-64bit      use 64-bit counters in UDP test packets

[KMG] indicates options that support a K/M/G suffix for kilo-, mega-, or giga-

iperf3 homepage at:
Report bugs to:

C:\Program Files\iperf>

For a Microsoft Windows system, you need only download the zip file for Windows, unzip the contents of the file, and then move the two files within the zip file, which are cygwin1.dll and iperf3.exe, if you downloaded a version 3 release of the software, to whatever directory you wish to keep the program in. Note: you can't test between a host running version 3 and one running version 2; both systems need to be running a version with the same major version unumber, e.g., a 2.x or 3.x version.

The download site offers 32-bit and 64-bit versions of the software. If you have a 32-bit version of Windows, you should use a 32-bit version and if you have a 64-bit version of Windows you should use the 64-bit version. If you don't know whether your version of Microsoft Windows is 32-bit or 64-bit, see Determining if your version of Windows is a 32-bit or 64-bit version.

To test with a public iperf3 server,, located in France, I could issue the command iperf3 -c using the iperf3 software installed on a Microsoft Windows system. Note: if you see the error message below, you may need to open a command prompt window in administrator mode to be able to test with iperf on the Windows system.

C:\Program Files\iperf>iperf3 -c
Connecting to host, port 5201
iperf3: error - unable to create a new stream: Permission denied

C:\Program Files\iperf>

To open a command prompt window where you can run the command with administrator permissions, see the instructions at Obtaining a Command Prompt on a Windows 8 System; the steps for other versions of Windows are similar.

If you run the software in client mode, you will see output similar to the following, which is from a test with the public test server

C:\Program Files\iperf>iperf3 -c
Connecting to host, port 5201
[  4] local port 49894 connected to port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec   512 KBytes  4.19 Mbits/sec
[  4]   1.00-2.00   sec  1.00 MBytes  8.39 Mbits/sec
[  4]   2.00-3.00   sec   896 KBytes  7.35 Mbits/sec
[  4]   3.00-4.00   sec  1.00 MBytes  8.39 Mbits/sec
[  4]   4.00-5.00   sec   896 KBytes  7.34 Mbits/sec
[  4]   5.00-6.00   sec   896 KBytes  7.33 Mbits/sec
[  4]   6.00-7.00   sec  1.00 MBytes  8.39 Mbits/sec
[  4]   7.00-8.00   sec   896 KBytes  7.34 Mbits/sec
[  4]   8.00-9.00   sec   896 KBytes  7.34 Mbits/sec
[  4]   9.00-10.00  sec  1.00 MBytes  8.40 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.00  sec  8.88 MBytes  7.44 Mbits/sec                  sender
[  4]   0.00-10.00  sec  8.87 MBytes  7.44 Mbits/sec                  receiver

iperf Done.

C:\Program Files\iperf>

For this particular test, the client system could achieve a bandwidth of about 7 - 8 Mbs, which was fairly good considering the client system was constrained by a 10 Mbs local area network (LAN) connection.


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