802.11r Fast Roaming configuration (channels and FT)


What is the best practice for setting up Wi-Fi channels on different nodes participating in one mobility domain? Should they have different channels or the same?
The information from different sources/guides differs also. Somebody says all should be the same, somebody vice versa.
I tried both options and didn't notice any significant difference.
What are the best practices/official recommendations on this?
Anything else to consider here?

Also, what is the best for FT - over DS or over the Air?
This setting also differs from a guide to guide and nobody really explains it, just "click this and that". But the majority of sources say over the Air is faster.

My understanding is each AP should have the same exact mobility domain, and the same SSID but on different non-overlapping channels. For example on 2.4ghz use channels 1,6 and 11. I've also heard that FT over the air is better.

You might read the discussions in this thread. It is not just about "faster", but if it works at all.

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I left the same channel for now, no issues so far...
Mainly because a lot of other Wi-Fis around and there is no such a big choice of good free channels. So if the same channel is good, then fine.

How to really test this?
I made iperf3 test while walking around the apartment, it seems pretty seamless.
But also, I didn't notice significant downtime without the Fast Roaming at all.
So my logic for now - not getting worse, let it be and I'll assume this is an improvement :slightly_smiling_face:

In the message that I linked:

Using that "Signal mapper" screen from Ubiquiti's Wifiman app helped a lot to notice the roaming actions.

And if you have enabled detailed logging in hostapd, you may get also system log lines like:

daemon.debug hostapd: wlan0: STA e0:...:30 WPA: FT authentication already completed - do not start 4-way handshake

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With Wifiman "Signal mapper" looks pretty good while walking around.

Also, I can see the logs like

FT authentication already completed - do not start 4-way handshake

Means everything is good in my case, I suppose.

As for the channels, I think there's no practical difference between the same or different non-overlapping. For sure, it is always better to use non-overlapping, speaking in general terms. But the reality may be slightly different, eg. in my case there are not enough free channels to pick a separate for each AP, but it works fine with the same one channel. So it will be better to overlap with my own AP than to overlap with several neighbors at once.

It is so far the only app that I have found, which clearly shows the FT transitions.

Sounds like you have a working FT, so be happy with the current settings :wink:

Thanks for helping.

Still can't understand why everybody says FT over the Air is faster (suppose both are working correctly).
Taking into account:

Over-the-Air—The client communicates directly with the target AP using IEEE 802.11 authentication with the FT authentication algorithm. Over-the-DS—The client communicates with the target AP through the current AP.

So if my APs are hard-wired, why over the air should be faster?
This approach supposes that [latency to the new AP over the air] < [latency to the current AP over the air + latency over the wire between two APs]
Latency over the wire can be ignored as it is usually < 1ms, so we left with [latency to the new AP over the air] < [latency to the current AP over the air]
But not sure this will always be true, or at least in most cases... Interesting thing.

After roaming is done does your device's throughput take a hit in any way? e.g. did you try doing any speedtest to see if the transfer rate remains like usual?

Reason I ask - whenever I have 802.11r enabled (and working, as I see FT authentication already completed - do not start 4-way handshake also), my android device takes a serious hit and throughput drops to something like 3Mbits/s. Interestingly enough, my iOS devices aren't impacted in any way.

I am starting to suspect it has something to do with my router model (or its chipset) that doesn't work well with OpenWrt's 802.11r....

I tried doing iperf3 (basically the same speed test but locally and more customizable) while walking around the house. Sometimes I saw a very short (1-2 sec) throughput drop to like 10 Mbps or so, but that was in the middle point between two APs, so the signal was really low from both, which is expected and not a Fast Roaming issue. As soon as I keep moving toward any AP, the speed increases to normal almost instantly.

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