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ewoodzy
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CAPsMAN: manual channel selection and DFS

Thu Sep 23, 2021 4:42 am

Trying to figure out how manual channel selection works on CAPsMAN for 5GHz, and how DFS affects things. It appears that I can set multiple channel frequencies for an interface (or channel preset), but it doesn't to play nice with DFS.
If I only specify DFS channels, channel selection works well -- setting the channel options for two APs to "5500,5660" will have one AP select 5500 and the other select 5660. I'd imagine the same would occur if I only selected non-DFS channels.

However, if I select both DFS and non-DFS channels (e.g: "5500,5660,5180"), both APs will immediately pick the non-DFS channel even if it's already crowded by other APs. This happens at interface enable time, manual channel re-selection and interval channel selection.

What I am trying to do is provide DFS and non-DFS channels to the AP, since DFS has room to avoid overlap, but while providing a channel to fallback on should the DFS range become unavailable. Is this actually possible to do or should I consider another channel configuration / live with some APs going down when they receive a DFS ping?

EDIT: My CAPsMAN network consists of three WAPac (RBwAPG-5HacT2HnD) units.
Last edited by ewoodzy on Thu Sep 23, 2021 9:16 am, edited 1 time in total.
 
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mkx
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Re: CAPsMAN: manual channel selection and DFS

Thu Sep 23, 2021 8:25 am

I'm only guessing here ...

However, if I select both DFS and non-DFS channels (e.g: "5500,5660,5180"), both APs will immediately pick the non-DFS channel even if it's already crowded by other APs.

Vast majority of users are unaware of DFS woes and freak out when they start APs and they don't come up immediately. Only few people are aware that if AP wants to use DFS channel, it's only normal to see delay before AP comes up. So I guess most wireless vendors implemented channel selection in a way it prefers non-DFS channels just to avoid users getting angry. And I guess this might be the case with Mikrotik as well.

I don't have experience with how MT AP does channel reselection ... does it monitor potential new channel in background? Probably not as DFS monitoring has to be thorough not to miss radar ping and with single receiver being busy while AP is active it is not possible to perform such a thorough monitoring in background. Which means AP has to disturb normal operations for a minute (or 10 depending on which DFS channel it's trying to pick) even during channel reselections. Which is not welcome either. And I guess that's why AP will never, if not forced to, reselect to a DFS channel.

So if you really want to use DFS channels (there are certainly some benefits of doing so), I guess you'll have to provide list of only DFS channels in order to force AP to actually pick one of them.
 
gotsprings
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Re: CAPsMAN: manual channel selection and DFS

Thu Sep 23, 2021 2:53 pm

Use create enable.

Then you can manually select a channel.
 
ewoodzy
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Re: CAPsMAN: manual channel selection and DFS

Fri Sep 24, 2021 8:16 am

Use create enable.

Then you can manually select a channel.
That works great for selecting a channel, or multiple exclusively DFS or non-DFS channels, but not a combination of both. That's the problem I'm having.

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