3 Linksys devices, help with wireless channel configuration

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humble_newbie
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Joined: 16 Oct 2020
Posts: 5

PostPosted: Fri Oct 16, 2020 13:45    Post subject: 3 Linksys devices, help with wireless channel configuration Reply with quote
Hi,

I normally dont post questions on forums unless I really cant find an answer and thats exactly where I am now. Hope one of you DDWRT masters can spare a minute and help out.

I have 3 linksys ddwrt devices all on the same subnet, all hardwired.

I am attempting to setup 3 non conflicting non overlapping 5 GHz/802.11ac (one one each device) VHT80 channels. The devices and ddwrt versions are as follows:

wrt1900acs: v3.0-r41771 std (12/21/19) - main router
wrt1900acs-v2: v3.0-r44048 std (08/02/20) - wireless access point
wrt1200ac-v2: v3.0-r44048 std (08/02/20) - wireless access point

Googling this question led me to understand that the channels to use are 42,58,106,122,155 as these dont overlap and therefore do not cause signal interference to each other... Except I dont have any of those in the channel list dropdown on the routers.

The closest I can get is, picking channel 42 for example, is to select channel 40 on the router and set the extension channel to UL (+2). Is this correct? Meaning, does this in fact set the channel to 42 as was intended?

Guys.. can someone please make my life easier and give me a quick reply with 3 channels and correct extensions for each?

Thanking you in advance.. and here's to hoping I am positing this in the right forum Smile
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humble_newbie
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Joined: 16 Oct 2020
Posts: 5

PostPosted: Fri Oct 16, 2020 13:53    Post subject: Reply with quote
should also add that all 3 of these are supposed to be broadcasting the same SSID with the same encryption.
ho1Aetoo
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Joined: 19 Feb 2019
Posts: 371

PostPosted: Fri Oct 16, 2020 14:32    Post subject: Reply with quote
42 is the 80mhz center channel and can not be selected directly in dd-wrt

in dd-wrt always select the primary 20mhz channel e.g. 36 and the 40mhz and 80mhz extension channel

a few examples:

primary 20mhz channel: 36
extension channel: UU +6
80mhz channel = 42 (upper +6)
40 mhz channel = 38 (upper)

primary 20mhz channel: 40
extension channel: UL +2
80mhz channel = 42 (upper +2)
40 mhz channel = 38 (lower)

primary 20mhz channel: 44
extension channel: LU -2
80mhz channel = 42 (lower -2)
40 mhz channel = 46 (upper)

primary 20mhz channel: 48
extension channel: LL -6
80mhz channel = 42 (lower -6)
40 mhz channel = 46 (lower)

everything is basically the same except that the 20mhz and 40mhz channels are different

Edit: no idea if this is true for Marvel? on Broadcom upper and lower are partially swapped, on Atheros it's correct
blkt
DD-WRT Guru


Joined: 20 Jan 2019
Posts: 1794

PostPosted: Fri Oct 16, 2020 14:41    Post subject: Reply with quote


Marvell channel extensions are the same as Atheros, not inverse or flipped like Broadcom.

36UU, 52UU, 100UU, 149UU (with four variants for each 80 MHz block, as ho1Aetoo explained).

Use UNII-1 and UNII-3 bands when possible.


Last edited by blkt on Fri Oct 16, 2020 15:05; edited 1 time in total
ho1Aetoo
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Joined: 19 Feb 2019
Posts: 371

PostPosted: Fri Oct 16, 2020 15:01    Post subject: Reply with quote
blkt wrote:
[img]
36UU, 52UU, 100UU, 149UU.


36UU, 52UU, 100UU, 116UU 149UU.

Quote:
Use UNII-1 and UNII-3 bands when possible


unfortunately you can't say that, it also depends on the regulatory domain (allowed frequencies and transmission power)

UNIII has in germany only 25mW (short range)

and DFS only plays a role if you have a weather radar (airport) nearby

usually the frequency range is completely unproblematic to use

the only difference is that stations can only scan passively, they have to wait until they receive a beacon from an AP
blkt
DD-WRT Guru


Joined: 20 Jan 2019
Posts: 1794

PostPosted: Fri Oct 16, 2020 15:20    Post subject: Reply with quote
ho1Aetoo wrote:
36UU, 52UU, 100UU, 116UU 149UU.
Then why stop there and ignore 132UU?
blkt wrote:
Use UNII-1 and UNII-3 bands when possible
ho1Aetoo wrote:
unfortunately you can't say that, it also depends on the regulatory domain (allowed frequencies and transmission power)
I defaulted to North America to match the chart and we don't know where OP is located. It's still good advice to avoid DFS range if in a big city, but especially when using Marvell routers.
ho1Aetoo
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Joined: 19 Feb 2019
Posts: 371

PostPosted: Fri Oct 16, 2020 15:28    Post subject: Reply with quote
blkt wrote:
ho1Aetoo wrote:
36UU, 52UU, 100UU, 116UU 149UU.
Then why stop there and ignore 132UU?


mhm... because depending on the region this is not a full 80mhz block


if you start at 132 the 80mhz would go from 5650mhz to 5730Mhz

and depending on the region e.g (5470 - 5725 @ 160), (N/A, 26), (N/A)

missing 5mhz for a 80mhz block

in short, it does not exist in germany, so I have forgotten it
blkt
DD-WRT Guru


Joined: 20 Jan 2019
Posts: 1794

PostPosted: Fri Oct 16, 2020 15:48    Post subject: Reply with quote
Haha sorry, I like to poke the bear with a stick.

Here is transmission power per country in case we never know OP's regulatory domain.

https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/tree/db.txt
WENED
DD-WRT Guru


Joined: 30 May 2017
Posts: 525
Location: Rural Manitoba

PostPosted: Fri Oct 16, 2020 17:04    Post subject: Reply with quote
blkt wrote:
Haha sorry, I like to poke the bear with a stick.

Here is transmission power per country in case we never know OP's regulatory domain.

https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/tree/db.txt


Good stuff blkt. Might also want to reference https://en.wikipedia.org/wiki/List_of_WLAN_channels

I had an interesting problem recently when I was using 2 5Ghz AP's where shortly after setting it up the 5Ghz went screwy on some of my routers.
At first I simply reverted to using one 5Ghz AP, but after thinking about it I remembered that one of AP's was on Ch 100 and the other on 149. I have retried the configuration but changed to using 36 and 149. So far all has been well with this. My reasoning is that because one of my AP's was on Ch 100 which is in the DFS range that somehow the system was detecting the signal as a radar signature and confusing the router. Just a thought but it's the best I can conclude.

_________________
WRT3200acm Master WDS 5GHz 80Mhz CH 36 (+6) r44048
Ath1 2.4Ghz Disabled
99 Static Leases

WRT3200acm r44048 WDS Station 5Ghz
Ath1 AP N/G Mixed Channel 11 HT40

WRT1900Ac V1 5Ghz r44048 WDS Station
(Defective, no 2.4Ghz but 5Ghz works great)

WRT1900AC V1 5Ghz AC 80Mhz WDS Station r44048
2.4Ghz AP Ch1 HT20 Mixed

(SPARE)WRT1900AC V1 r44048 On LAN
5Ghz WDS AP Ch149(+6) 80Mghz
2.4Ghz Ch 6 20Mhz N/G Mixed

WRT1200AC V1 r44048 LAN
2.4Ghz 20Mhz Ch 6 Mixed
5 Ghz 80Mhz Ch 149 (UUU+6) WDS AP

WRT54G DD-WRT v3.0-r37305 micro AP CH 6 Mixed - Not in use

3200 Master -> LAN -> 1200 V1 -> WDS 5Ghz -> 1900 V1 & 1900V1
3200 Master -> WDS -> 3200 Slave
humble_newbie
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Joined: 16 Oct 2020
Posts: 5

PostPosted: Fri Oct 16, 2020 17:56    Post subject: Reply with quote
Thanks everyone for the help! I got it working and so far so good!
ho1Aetoo
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Joined: 19 Feb 2019
Posts: 371

PostPosted: Fri Oct 16, 2020 18:22    Post subject: Reply with quote
WENED wrote:
I have retried the configuration but changed to using 36 and 149. So far all has been well with this. My reasoning is that because one of my AP's was on Ch 100 which is in the DFS range that somehow the system was detecting the signal as a radar signature and confusing the router. Just a thought but it's the best I can conclude.


I don't think so, DFS (dynamic frequency selection) works like this

an AP located in the DFS frequency range scans periodically for high power radar pulses
if the AP detects radar pulses it changes the channel to a non-DFS channel


the real problem is that the clients in the DFS area are only allowed to scan passively, they are only allowed to scan when they receive a beacon from an AP, so roaming between AP's is slower

is therefore only relevant if you run multiple AP's
ho1Aetoo
DD-WRT User


Joined: 19 Feb 2019
Posts: 371

PostPosted: Fri Oct 16, 2020 19:09    Post subject: Reply with quote
https://www.wi-fi.org/knowledge-center/faq/what-are-passive-and-active-scanning
WENED
DD-WRT Guru


Joined: 30 May 2017
Posts: 525
Location: Rural Manitoba

PostPosted: Fri Oct 16, 2020 22:46    Post subject: Reply with quote
ho1Aetoo wrote:
WENED wrote:
I have retried the configuration but changed to using 36 and 149. So far all has been well with this. My reasoning is that because one of my AP's was on Ch 100 which is in the DFS range that somehow the system was detecting the signal as a radar signature and confusing the router. Just a thought but it's the best I can conclude.


I don't think so, DFS (dynamic frequency selection) works like this

an AP located in the DFS frequency range scans periodically for high power radar pulses
if the AP detects radar pulses it changes the channel to a non-DFS channel


the real problem is that the clients in the DFS area are only allowed to scan passively, they are only allowed to scan when they receive a beacon from an AP, so roaming between AP's is slower

is therefore only relevant if you run multiple AP's


I hear and fully understand what you are saying. Incidentally I have over 50 years of experience in electronics so what you are saying makes sense if I was speaking about client connection. However if you review what I said you will see that I was referring exclusively to the routers. The two routers in question have < 5' spacing and since I changed the AP channels to outside of DFS channels I have encountered no problems. The only reason I was using Channel 100 +6 was due to a need at one time to have a VAP on the client Router and since VAP's on a client will only function on Channel 100+ I had no choice. Since I decided to run the second Router with a 5Ghz AP, I no longer had a need for using Channel 100 on my primary router.
I do thank you however for your input and appreciate that I may not have clear about my observations. If I was absolutely convinced that a problem existed with the particular configuration I would open a ticket accordingly, but since it was only an observation I just threw it out there in the event someone else might be experiencing the same strange behavior.

_________________
WRT3200acm Master WDS 5GHz 80Mhz CH 36 (+6) r44048
Ath1 2.4Ghz Disabled
99 Static Leases

WRT3200acm r44048 WDS Station 5Ghz
Ath1 AP N/G Mixed Channel 11 HT40

WRT1900Ac V1 5Ghz r44048 WDS Station
(Defective, no 2.4Ghz but 5Ghz works great)

WRT1900AC V1 5Ghz AC 80Mhz WDS Station r44048
2.4Ghz AP Ch1 HT20 Mixed

(SPARE)WRT1900AC V1 r44048 On LAN
5Ghz WDS AP Ch149(+6) 80Mghz
2.4Ghz Ch 6 20Mhz N/G Mixed

WRT1200AC V1 r44048 LAN
2.4Ghz 20Mhz Ch 6 Mixed
5 Ghz 80Mhz Ch 149 (UUU+6) WDS AP

WRT54G DD-WRT v3.0-r37305 micro AP CH 6 Mixed - Not in use

3200 Master -> LAN -> 1200 V1 -> WDS 5Ghz -> 1900 V1 & 1900V1
3200 Master -> WDS -> 3200 Slave
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