DD-WRT selecting invalid 80 MHz channels on 5 GHz

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HydroxideEncore
DD-WRT Novice


Joined: 01 Sep 2019
Posts: 2

PostPosted: Sun Sep 08, 2019 8:42    Post subject: DD-WRT selecting invalid 80 MHz channels on 5 GHz Reply with quote
I'll preface this with the fact that I have very little knowledge of networking - I just like to tinker... I only figured this out after a few days of wondering why things worked and then stopped working.

I'm using r40854 on Linksys WRT32X.

I've discovered that on occasion, DD-WRT selects channels which are not valid at 80 MHz width on 5 GHz if I leave wireless channel selection on Auto.

I noticed that DD-WRT sometimes selects channel 104 automatically. This causes issues - my Samsung S7 Edge only connects at 20 MHz width, and my Chromecast does not connect at all to the 5 GHz network.

I can replicate the issue if I manually select channels 104 or 110, both UU (+6).

If I manually select channel 100 or 116, the problems disappear.

I'm not sure if this has been reported before - I did a quick Google, but nothing on the first page seemed relevant.

I would like to remain on Auto so that Radar Detection can move me away from any channels being used for radar, but perhaps DD-WRT can move me to a valid 80 MHz channel?

I've read a tiny amount and seem to think that there are valid and invalid channels based on channel width - maybe DD-WRT can force selection of valid channels, manually or otherwise, based on channel width?

Has a more recent build fixed this?
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kernel-panic69
DD-WRT Guru


Joined: 08 May 2018
Posts: 11802
Location: Texas, USA

PostPosted: Sun Sep 08, 2019 10:56    Post subject: Reply with quote
It's a given not to use Auto channel in DD-WRT and why you use a wi-fi analyzer to pick your channels. This is something that will probably never change, I have not seen any work being done to 'fix' this.
Yemble
DD-WRT Guru


Joined: 17 Feb 2010
Posts: 611
Location: Yorkshire (GOC)

PostPosted: Sun Sep 08, 2019 13:48    Post subject: Reply with quote
Read this: http://www.emperorwifi.com/2015/09/the-limitations-of-channel-144.html
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HydroxideEncore
DD-WRT Novice


Joined: 01 Sep 2019
Posts: 2

PostPosted: Sun Sep 08, 2019 20:17    Post subject: Reply with quote
Yemble wrote:
Read this: http://www.emperorwifi.com/2015/09/the-limitations-of-channel-144.html


Thanks for the link. DD-WRT doesn't change my channel automatically to 144. It was an observation I made that it would sometimes automatically select an 80 MHz channel 104-116, which seems to mess things up. It just seemed strange that this would cause connection issues.

Reading around, it does seem that 100-112, 116-128 and 132-144 are the only valid 80 MHz channels.

Just curious and noted an observation, in case it was useful...

kernel-panic69 wrote:
It's a given not to use Auto channel in DD-WRT and why you use a wi-fi analyzer to pick your channels. This is something that will probably never change, I have not seen any work being done to 'fix' this.


Noted, thank you - with my stumblings, I figured as much.
johnnyNobody999
DD-WRT User


Joined: 10 Jan 2014
Posts: 444

PostPosted: Tue Oct 01, 2019 18:12    Post subject: Reply with quote
Does anyone use radar detection on the WRT3200ACM? I see a check box for it on both the 5GHz AP and Client/Station settings. I would assume that it's non-functional on the Client/Station. Also, I've read that ath2 has to be enabled to use radar detection. Why would one need ath2 enabled if there's a check box for radar detection for the AP (in my case ath0)? It's a confusing issue. I don't see anything that gives a current tutorial for radar detection setup.
blkt
DD-WRT Guru


Joined: 20 Jan 2019
Posts: 3441

PostPosted: Tue Oct 01, 2019 22:54    Post subject: Reply with quote
That third radio (ath2) is designed only to listen for signals and if detected it forces your router to vacate the DFS frequency range. I would avoid using that range altogether if DFS detection is enabled as it's very sensitive and prone to false positives.

The other function you are talking about is trying to it as a normal radio, against the original design purpose (receive only, internal antenna, shares MAC address with ath1).
johnnyNobody999
DD-WRT User


Joined: 10 Jan 2014
Posts: 444

PostPosted: Wed Oct 02, 2019 1:24    Post subject: Reply with quote
blkt wrote:
That third radio (ath2) is designed only to listen for signals and if detected it forces your router to vacate the DFS frequency range. I would avoid using that range altogether if DFS detection is enabled as it's very sensitive and prone to false positives.

The other function you are talking about is trying to it as a normal radio, against the original design purpose (receive only, internal antenna, shares MAC address with ath1).


I tried to use a static channel but the config went back to auto channel on a reboot.
PIZZEDMEOFF
DD-WRT User


Joined: 12 Dec 2017
Posts: 243
Location: FL

PostPosted: Wed Oct 02, 2019 12:02    Post subject: Reply with quote
johnnyNobody999 wrote:
I tried to use a static channel but the config went back to auto channel on a reboot.


after every change you make hit save when done hit apply see if that makes it stick

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SVN Timeline:
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Commands:
Misc: sleep 10;stopservice nas;stopservice wlconf;startservice wlconf;startservice nas
samba: { sleep 30; stopservice samba3; startservice samba3; } &

WRT1900ACv1:

WIFI: 2.4ghz: NG-mixed, 20mhz channel width, channel follows AP, WPA2-CCMP-128.
WIFI: 5ghz: AC/N mixed, 40mhz channel width, channel 100+upper, WPA2-CCMP-128.
Misc Info: WPA2 Personal: "CCMP-128 (AES)" Static IP's VIA Mac+Host, SFE Enabled, No Rebind, Strict, no-resolv. NOTE: this is now just a wireless access point so to speak but all settings still apply to what ever wireless person connects.
johnnyNobody999
DD-WRT User


Joined: 10 Jan 2014
Posts: 444

PostPosted: Wed Oct 02, 2019 15:46    Post subject: Reply with quote
blkt wrote:
That third radio (ath2) is designed only to listen for signals and if detected it forces your router to vacate the DFS frequency range. I would avoid using that range altogether if DFS detection is enabled as it's very sensitive and prone to false positives.

The other function you are talking about is trying to it as a normal radio, against the original design purpose (receive only, internal antenna, shares MAC address with ath1).


There's an article somewhere where BrainSlayer was using radar detection on his network and he said everything works fine. I'd have to search for that post again but I'm too lazy to do so. If there were up-to-date wikis a lot of confusion would be eliminated. Searching through posts and/or web searches or IRC aren't always the best way to get info - especially when there is conflicting info. But, you get what you pay for.......
johnnyNobody999
DD-WRT User


Joined: 10 Jan 2014
Posts: 444

PostPosted: Wed Oct 02, 2019 15:49    Post subject: Reply with quote
d0ug wrote:
AFAIK you can use any channel you want within the limitations of the top or bottom end of the band, that you cannot extend above or below the legal limits. This is why dd-wrt has the extension channel option with U for upper and L for lower. So if you pick a particular channel and choose the UL option, then you will be centered on the channel you choose and the wider band will extend into the channel above and below you chosen channel. Or if you pick UU, your chosen channel will be the bottom end of the channel and you will extend into the two channels above your chosen channel.

Just like with 802.11b/g/n people will usually suggest that you only use channels 1 6 or 11 because they are the only non-overlapping channels, but you can otherwise still set your wifi to use whatever channel that you want. It should be perfectly possible to use any channel you want in the 5ghz band. The suggestions you see on a lot of pages are just like the channel 1, 6 or 11 suggestions for 802.11b/g/n. They are the only guaranteed non-overlapping channels for whatever particular bandwidth you are using.


It would be great if there was a "slam-dunk" automatic channel selection that would change channels automatically if some kind of interference popped up.
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