11ac clients and daul band wireless environment

[Bwilson13]

Good morning mobility community,

I am trying to figure out the best way to prevent 11ac clients (Lenovo X1 carbon 6th gen running Windows 10 x64) from connecting to 802.11n on a specific SSID.  I have enabled client band select on the SSID to make the 5 Ghz band more attractive to the clients but every now and again a client will connect using 802.11n.  I also realize that not all wireless clients are created equal as it relates to algorithms used in each client.  I did find an old forum post in community about disabling WMM on a guest WLAN but it looks like it needs to be an open SSID.  The SSID in my environment is for enterprise end-users and it's not open.  Is WMM still the best way to remove .11n or is there another way?

Thanks,

Bruce

[Leo Laohoo]

Disable WMM on a per-SSID basis will disable 802.11n and 802.11ac.

[Bwilson13]

Thanks Leo!  It seems then that disabling WMM isn't viable.   I assume the next best thing to review is only using 5 Ghz in the wireless network?

[patoberli]

What do you have against those clients connecting to 2.4 GHz? Assuming you have enabled 40 MHz or even 80 MHz channels on 5 GHz, the client typically prefers the 5 GHz. If you use for spectrum reasons just 20 MHz channels, then the client won't gain a lot by connecting to the (typically) weaker 5 GHz signal instead of 2.4 GHz and thus often prefers the 2.4 band.

With Intel based clients you can configure the driver to prefer 5 GHz, but that also doesn't always help.

[Bwilson13]

I personally have nothing against them connecting on 2.4 even though more things operate on that band.  It's a constant battle with trying to get other folks to understand why a client is choosing 2.4 over 5.  And I'm not using set channel widths the WLC is dynamically managing the channel width via RRM.  Just to add I'm not an wireless/RF expert but am thankful for your insight and knowledge sharing!

I did look at the Intel 8265 dual band NIC settings on the X1 and the wireless mode for 802.11n/ac is set to ac. The only other options are to set it to 11n or disable.

[patoberli]

There should be an option which one to prefer, the option is named "Preferred Band". There you can choose 5.2 GHz, that should put more priority into that band.

[Some_Guy]

@patoberli wrote:

What do you have against those clients connecting to 2.4 GHz? Assuming you have enabled 40 MHz or even 80 MHz channels on 5 GHz, the client typically prefers the 5 GHz. If you use for spectrum reasons just 20 MHz channels, then the client won't gain a lot by connecting to the (typically) weaker 5 GHz signal instead of 2.4 GHz and thus often prefers the 2.4 band.

Agreed, this has been my experience as well, with current-day client devices. Most stuff nowadays seems to be fairly good about preferring 5 GHz unless it is in a situation where the 5 GHz signal truly is no better. It's not like the old days anymore, where clients were insanely stupid and just grabbed whatever they could hear based solely on RSSI.

I used to use only 5 GHz for internal clients, and only 2.4 GHz for guest clients, but we've actually been migrating towards everything being dual-band since clients nowadays seem to be handling dual-band reasonably.

"Client band select" is a dirty hack at best and causes more headaches than it solves. It is very intrusive. It may have been helpful back in the days of super idiotic clients, but is no longer necessary IMO. There are less intrusive ways of helping modern clients make decisions.

When disabling the lowest data rates, I like to be slightly more aggressive at disabling on 2.4 GHz than on 5 GHz. E.g. if I'm disabling legacy rates below 18 Mbps on 5 GHz, then I will disable up to 24 Mbps on 2.4 GHz. I also disable the corresponding MCS indices for n/ac. E.g. if I disable the legacy rates that use QPSK modulation, then I also disable all the n/ac MCSes that use QPSK modulation. Enabling 802.11k and 802.11v is also helpful. And of course, I turn off the 2.4 GHz radio in a lot of the APs (probably about two-thirds of APs on average).

After all that, if a modern client still chooses 2.4 GHz, then it usually is not actually that bad of a choice in the specific situation.

[Leo Laohoo]

Depending on the model of the WLC, there is an per-SSID option to limit the bandwidth of the wireless client on a per-SSID basis or per-client basis.