Channel width change on 2.4GHz radio band is not supported

[jguittet]

Hello

I have a C9120AXE access point. I'm trying to change the bandwith using SSH command: "ap name AP84F1.4783.21FC dot11 dual-band channel width 40W" but it fails with the following error printed on the serial console: "%RRM_CLIENT-3-EWLC_EXEC_ERR: Chassis 1 R0/0: wncd: % Error: AP AP84F1.4783.21FC MAC: 84f1.47ad.1160 Slot-id 0 - Channel width change on 2.4GHz radio band is not supported"

Which settings (WebUI or terminal) should I change to allow changing the bandwith ?

Thanks

Joel

[Leo Laohoo]

2.4 Ghz will only support 20 Mhz channel bond.  

[jguittet]

A colleague done this on this AP in the past so I know it's possible. The AP has been reset to factory defaults in the mean time.

[Leo Laohoo]

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@jguittet wrote:
A colleague done this on this AP in the past so I know it's possible.

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Yes, it was possible with very old model of APs running equally old firmware.  I remembered CAP1250 could be done with 7.0.X.X.  

Do understand the logic as to why 40 Mhz channel bond in 2.4 Ghz is disabled.  

[Rasika Nayanajith]

You will have better Wi-Fi experience by keeping it only 20MHz. Do not have 40MHz channels in 2.4GHz band

HTH
Rasika
*** pls rate all useful responses ***

[jguittet]

Hello,

I understand that but I should share a bit of the context: we are developing a wifi device and testing with various wifi configuration is required by the customer with several APs, including this Cisco model.

Tests include 40MHz bandwidth on the 2.4GHz band. So I'm looking how to do it.

Thanks

Joel

[Gaurav Kansal]

Dear jguittet,

Because we don't have enough non-overlapping channels in 2.4 Ghz, and to DCA work properly while allotting channels to neighboring APs so they can't interfere each other, so channel bonding in 2.4 GHz is disabled now days. If you achieve 40 Mhz then you cannot avoid channel interference in your topology as you invited this with yourself.    

GoodLuck
Regards
Gaurav Kansal

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[jguittet]

Hello @kansal

Thanks for the reply. So if my understanding is correct this is disabled in recent firmware ? I recently move from 16.x to 17.3. Is it explaining why I cannot set 40MHz bandwidth ?

Thanks for the clarification,

Joel

[JPavonM]

@jguittet bonding channels in 2.4 GH band, or using channels other than 1,6 and 11 is a BAD PRACTICE so please do not do it even if it's possible to avoid impacting your neighbour's networks.

[jguittet]

@JPavonM I understand that

Just to remember the purpose of this request: I'm developing a wifi device for a customer, and we have a test suite covering this use case in case the device is in front of an AP configured with 40MHz bandwidth in the field, which I cannot manage myself because devices are worldwide and even if it is a bad practice, it doesn't prevent someone to do it.

The test suite was executed perfectly before I have done an update + factory reset of the configuration so I would like to recover the possibility to do it.

But if you indicate me this is totally blocked in latest firmware because it is a bad pactise, this is fine for me. I need the confirmation of this hypothesis to indicate my customer this use case cannot be covered anymore with the Cisco AP in this case.

Thanks

[JPavonM]

@jguittet you can find a paragraph abot this int he C9800 Best Practices guide (https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/technical-reference/c9800-best-practices.html#Channelwidth):

Here the term "legacy radios" refers to legacy APs, or running legacy software.

●   20 MHz: Permits the radio to communicate using only 20-MHz channels. Choose this option for legacy 802.11a radios, 20-MHz 802.11n radios, or 40-MHz 802.11n radios that you want to operate using only 20-MHz channels.

●     40 MHz: Permits 40-MHz 802.11n/ac/ax radios to communicate using two adjacent 20-MHz channels bonded together.

If you need and official document then ask your AM/SE about it.

[jguittet]

@JPavonM not bad. but how to configure it ?

Which settings (WebUI or terminal) should I change to allow changing the bandwith ?

Currently I'm in front of this:

Thanks for the support

[JPavonM]

Unfortunately there is no such option in the 2.4 RF Profiles:

But it is there in 5 GHz profile: