• Troubleshooting WiFi Throughput Issues with iPerf3 on Arista APs

 
 
Print Friendly, PDF & Email

Introduction

When we observe low throughput in the network it is important to understand whether the issue lies on the WiFi or the wired side of the network. The method to achieve this is to perform an iPerf test and compare results. This utility is present on the Arista AP which acts as an iPerf server, eliminating the need for a second client connected to the WiFi network.

Online speed tests are good for quick results; however, they are not ideal for troubleshooting as these speed tests are also dependent on factors outside the LAN/WLAN.

Prerequisites

  • config shell CLI access to the Arista AP.
  • A wireless client with iPerf utility installed.

Solution

Run iPerf on an Arista AP

  • Log in to the AP config shell CLI and execute the command –
    [config]$ debug iperf3
  • When prompted to input the arguments, enter ‘-s’. This will enable the iPerf server mode on the AP and opens a local UDP port 5201 (default) for the incoming connection. You can press Ctrl+C to interrupt the test.
  • On the client laptop, enter the following command:
    # iperf -c 172.17.30.1

    With this command we are running iPerf in client mode and instructing it to connect to the server 172.17.30.1 which is the IP address of the AP, running in iPerf server mode.

  • You can modify the test with multiple arguments on the client side, based on the iPerf documentation: https://iperf.fr/iperf-doc.php

Results

Example of the command run on the iPerf server (AP):

[config]$ debug iperf3

Enter iperf3 input arguments : -s

Executing iperf3.....Press Ctrl+C to quit

-----------------------------------------------------------

Accepted connection from 172.17.30.134, port 53520

[ 6] local 172.17.30.136 port 5201 connected to 172.17.30.134 port 53521

[ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams

[ 6] 0.00-1.00 sec 23.2 MBytes 195 Mbits/sec 0.023 ms 58888/75563 (78%)

[ 6] 1.00-2.00 sec 23.1 MBytes 194 Mbits/sec 0.104 ms 59961/76531 (78%)

[ 6] 2.00-3.00 sec 22.0 MBytes 185 Mbits/sec 0.061 ms 43800/59619 (73%)

[ 6] 3.00-4.00 sec 21.6 MBytes 181 Mbits/sec 0.067 ms 47215/62745 (75%)

[ 6] 4.00-5.00 sec 24.1 MBytes 202 Mbits/sec 0.044 ms 51345/68624 (75%)

[ 6] 5.00-6.00 sec 26.0 MBytes 218 Mbits/sec 0.146 ms 62732/81408 (77%)

[ 6] 6.00-7.00 sec 26.3 MBytes 221 Mbits/sec 0.024 ms 59882/78762 (76%)

[ 6] 7.00-8.00 sec 28.4 MBytes 238 Mbits/sec 0.055 ms 60323/80719 (75%)

[ 6] 8.00-9.00 sec 27.5 MBytes 231 Mbits/sec 0.094 ms 63220/82967 (76%)

[ 6] 9.00-10.00 sec 25.6 MBytes 215 Mbits/sec 0.035 ms 63207/81616 (77%)

[ 6] 10.00-10.02 sec 480 KBytes 188 Mbits/sec 0.026 ms 0/337 (0%)

- - - - - - - - - - - - - - - - - - - - - - - - -

[ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams

[ 6] 0.00-10.02 sec 1.02 GBytes 875 Mbits/sec 0.026 ms 570573/748891 (76%)

 

Example of the command run on the iPerf client:

[root@admin ~]# iperf -c 172.17.30.1

 

Note:

  • Each wireless client may have different capabilities, yielding different throughput results. Therefore, it is recommended to perform iPerf tests from multiple clients and preferably clients running different operating systems i.e. Windows, iOS, Android etc.
  • Ideally, use hardware with the latest wireless capabilities to perform iPerf tests, in order to benchmark the throughout over the wireless medium.
  • It is also important to keep the following parameters in mind, which are directly responsible for the throughput achieved.
    • MCS Index negotiated by the client.
    • Spatial streams supported by the client.
    • Channel width – whether 20 MHz, 40 MHz, 80 MHz or 160MHz.
    • Guard Interval.
  • This is an example of a quick reference chart to determine throughput that can be expected with various combinations of hardware capabilities and wireless configuration.
Follow

Get every new post on this blog delivered to your Inbox.

Join other followers: