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    “Wireless clients are experiencing very slow speed” ,   is a common  problem on a wireless lan environment.

    As part of troubleshooting this, we got to take care of

    • 1)      Low Signal Strength.
    • 2)      Low SNR.
    • 3)      Insufficient Data rate.
    • 4)      Packet Drop.
    • 5)      Interference.
    • 6)      Client Driver problem.
    • 7)      QoS related problem.
    •       Problem with Roaming.
    • 9)      OR  Any configuration related problem.

    During the course of troubleshooting, we do need a way to test the throughput, as and when we make any changes.

    IPERF comes as a very handy tool. This can easily tell us the speed of data transfer.

    Here are the details for the IPERF test.

    Test Setup

    1. Download the IPERF exe from the following URL.
    2. Setup a wired computer to serve as a “server”.
    3. Take a copy of all the downloaded files (“iperf.exe and the supporting dll files) and have it on a new folder(IPERF) in the C:/ drive.
    4. Setup a wireless computer to serve as a “client”.
    5. Take a copy of all the downloaded files (“iperf.exe and the supporting dll files) and have it on a new folder(IPERF) in the C:/ drive.

    Test Procedure

    • 1) On the wired PC “ the IPERF server”, run the command   " iperf.exe –s  ".


    iperf s.jpg


    • 2)      Connect the Wireless PC  “the IPERF client”  to the SSID in question.
    • 3)      Execute the command " iperf.exe – c  <IP address of the server>   -P 10  -w 1000k "

                   (  -P refers to the number of parallel TCP streams and –w referes to the TCP window size  )

    iperf c.jpg


    • 4)  Repeat the test 3 to 4 time in a gap of 2 minutes.
    • 5)  Every time when you run the test, get the output “ show client detail <MAC of the wireless client>
    • 6)  Collect the outputs and send it across to the engineer.

    What is Iperf?

    Iperf was orginally developed by NLANR/DAST as a modern alternative for measuring TCP and UDP bandwidth performance.

    Iperf is a tool to measure maximum TCP bandwidth, allowing the tuning of various parameters and UDP characteristics. Iperf reports bandwidth, delay jitter, datagram loss.

    Iperf features

    * TCP

    • * Measure bandwidth
    • * Report MSS/MTU size and observed read sizes.
    • * Support for TCP window size via socket buffers.
    • * Multi-threaded if pthreads or Win32 threads are available. Client and server can have multiple simultaneous connections.

    * UDP

    • * Client can create UDP streams of specified bandwidth.
    • * Measure packet loss
    • * Measure delay jitter
    • * Multicast capable
    • * Multi-threaded if pthreads are available. Client and server can have multiple simultaneous connections. (This doesn't work in Windows.)

    * Where appropriate, options can be specified with K (kilo-) and M (mega-) suffices. So 128K instead of 131072 bytes.

    * Can run for specified time, rather than a set amount of data to transfer.

    * Picks the best units for the size of data being reported.

    * Server handles multiple connections, rather than quitting after a single test.

    * Print periodic, intermediate bandwidth, jitter, and loss reports at specified intervals.

    * Run the server as a daemon.

    * Run the server as a Windows NT Service

    * Use representative streams to test out how link layer compression affects your achievable bandwidth.

    Level 1
    Level 1

    does the goodput is also can be meausured by iperf?

    Level 1
    Level 1

    thanks for your input victor,

    did you have any tips for troubleshooting or conformation for a customer?

    thanks raffa
    Community Member

    It might be helpful to update this article to reflect that the engineer will probably want the iperf output from the client side as well as the output from 'show client detail <mac>' from the wireless controller. 

    Cisco Employee
    Cisco Employee



    here which is the server ip and which the client IP




    Michael Hubbard
    Level 1
    Level 1

    Thanks Victor!

    Here is a link to a blog I did for iPerf3. 


    The US DoE now develops iPerf and version 3 is much improved. They also have a suite of tools called Perfsonar that is amazing -


    Jerry Olla from Wireless LAN Professionals has a project using a NanoPi NEO2 for iPerf testing. It's about $100 total for the Neo, the portable battery and USB AC adapter.

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