C9800CL speed limit

[sunhailun]

Hi guys, I recently migrated from vWLC to C9800CL, took me a while to get use to the new platform but luckly so far so good. One interesting issue through, when testing the speed over 802.11ac 5ghz, it seems like there is a bottle neck at 500mbps. I have tested like 30+ times using local deployed iperf testing platform, I can only get somewhere around 450-490mbps max. Barely reach 500mbps.

I have tried both with FlexConnect and local mode, almost the same result. Actually it is a bit slower on local mode. My ISP provides 1000mbps speed, and here is the funny part. When I first migrate to the 9800 platform, I didn't deploy it correctly by disabling SVI but using gi1 as the only port to handling traffics, with that I can get about 700-750mbps speedtest, but since it is not the correct way to use 9800, I am not able to get the correct ipv6 address, so I corrected it and put gi1 port as trunk and let SVI to handle all traffc as designed. But now I hit the bottle neck.

What could be the issue here? Any ideas? Thanks

Attaching the screenshot of local iperf test result, as you can see the upload speed is even higher than the download.And this is tested with minimum interference as possible, meaning close the where the AP is located, connect to 5g and assign to 80mhz...

[marce1000]

     - FYI : https://www.cisco.com/c/en/us/support/docs/wireless/wireless-lan-controller-software/220877-troubleshoot-wireless-speed-issues.html
      Also have a checkup of the C9800CL wireless controller's configuration with the CLI command 
     show tech wireless and feed the output from that into : Wireless Config Analyzer

  M.

[sunhailun]

Update more info:

I have enabled, mDNS, multicast for Apple TV, AirPlay, AirPrint...etc.

AVC is enabled, but I have tested with both on and off, not much of difference interms of speed test.

QoS is set to FT - platinum.

SSID security is using WPA2 psk.

FlexConnect mode with central switching, chentral DHCP and central authentication

C9800-CL firmware 17.12.03 (tried 17.09.05 same result)

5 x 3802i AP

All hosted on esxi 8.0 with 4 core CPU, 8g ram and 16gb hard disk as required for small deployment.

Thanks

[JPavonM]

That speed that you mention matches the current capabilities of 802.11ax clients but depending on the channel width that you will be using that link speed can be different. It seems to me you were using 80MHz channel width to get that 700 Mbps link speed.

First, it is not best practice to use 80MHz channel widths in 5GHz band but only 40 MHz width as much. Second, link speed depend on multiple facts like distance to the AP, noise, interference, occupancy, utilization, ... so performing iPerf tests is not the best way to measure that (additionally using iPerf3 with Windows is not recommended as it does not use the native libraries). Third, if the iPerf server is our of the corporate netowrk, that would also impact the results, so best deploy a server internally, and close to the AP/WLC so to avoid bottle necks from L3 devices and/or firewalls. (Even with the appropiatte setup, it would be hard to get link speeds above 5xx Mbps, and throughputs greater than 350 Mbps)

[jagan.chowdam]

Check client MCS rate and then verify it against MCS Table. https://mcsindex.com/

Refer the link below to understand MCS table and how to read it.

https://wlanprofessionals.com/mcs-table-and-how-to-use-it/

Jagan Chowdam