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#1 2017-09-25 03:24:19

alex.forencich
Member
Registered: 2011-05-29
Posts: 96

[SOLVED] Why is my wifi getting downgraded to 20 MHz channel width?

I'm trying to get my wireless connection running with a 40 MHz channel width.  However, it seems to only connect at 20 MHz, with the next-to-useless message "capabilities/regulatory prevented using AP HT/VHT configuration, downgraded".  My reg domain appears to be set correctly, and both involved devices appear to be advertising HT20/HT40.  What gives? 

Router is a Netgear WNDR4300 running dd-wrt, wi-fi card is an Intel Wireless-AC 7260.

relevant dmesg on connecting:

[ 1878.524221] wlan0: authenticate with 10:xx:xx:xx:xx:9d
[ 1878.524232] wlan0: capabilities/regulatory prevented using AP HT/VHT configuration, downgraded
[ 1878.526756] wlan0: send auth to 10:xx:xx:xx:xx:9d (try 1/3)
[ 1878.528275] wlan0: authenticated
[ 1878.530488] wlan0: associate with 10:xx:xx:xx:xx:9d (try 1/3)
[ 1878.532717] wlan0: RX AssocResp from 10:xx:xx:xx:xx:9d (capab=0x11 status=0 aid=2)
[ 1878.534605] wlan0: associated

iw dev, showing 20 MHz width:

$ iw dev
phy#0
	Interface wlan0
		ifindex 4
		wdev 0x1
		addr e8:xx:xx:xx:xx:13
		ssid xxx-n
		type managed
		channel 161 (5805 MHz), width: 20 MHz, center1: 5805 MHz
		txpower 22.00 dBm

iwconfig:

$ iwconfig wlan0
wlan0     IEEE 802.11  ESSID:"xxx-n"  
          Mode:Managed  Frequency:5.805 GHz  Access Point: 10:xx:xx:xx:xx:9D   
          Bit Rate=130 Mb/s   Tx-Power=22 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=44/70  Signal level=-66 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:204   Missed beacon:0

iw phy showing HT20/HT40 capability for 40 MHz channel width:

$ iw phy
Wiphy phy0
	max # scan SSIDs: 20
	max scan IEs length: 425 bytes
	max # sched scan SSIDs: 20
	max # match sets: 11
	max # scan plans: 2
	max scan plan interval: 65535
	max scan plan iterations: 254
	Retry short limit: 7
	Retry long limit: 4
	Coverage class: 0 (up to 0m)
	Device supports RSN-IBSS.
	Device supports AP-side u-APSD.
	Supported Ciphers:
		* WEP40 (00-0f-ac:1)
		* WEP104 (00-0f-ac:5)
		* TKIP (00-0f-ac:2)
		* CCMP-128 (00-0f-ac:4)
		* CMAC (00-0f-ac:6)
	Available Antennas: TX 0 RX 0
	Supported interface modes:
		 * IBSS
		 * managed
		 * AP
		 * AP/VLAN
		 * monitor
		 * P2P-client
		 * P2P-GO
		 * P2P-device
	Band 1:
		Capabilities: 0x11ee
			HT20/HT40
			SM Power Save disabled
			RX HT20 SGI
			RX HT40 SGI
			TX STBC
			RX STBC 1-stream
			Max AMSDU length: 3839 bytes
			DSSS/CCK HT40
		Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
		Minimum RX AMPDU time spacing: 4 usec (0x05)
		HT Max RX data rate: 300 Mbps
		HT TX/RX MCS rate indexes supported: 0-15
		Bitrates (non-HT):
			* 1.0 Mbps
			* 2.0 Mbps (short preamble supported)
			* 5.5 Mbps (short preamble supported)
			* 11.0 Mbps (short preamble supported)
			* 6.0 Mbps
			* 9.0 Mbps
			* 12.0 Mbps
			* 18.0 Mbps
			* 24.0 Mbps
			* 36.0 Mbps
			* 48.0 Mbps
			* 54.0 Mbps
		Frequencies:
			* 2412 MHz [1] (22.0 dBm)
			* 2417 MHz [2] (22.0 dBm)
			* 2422 MHz [3] (22.0 dBm)
			* 2427 MHz [4] (22.0 dBm)
			* 2432 MHz [5] (22.0 dBm)
			* 2437 MHz [6] (22.0 dBm)
			* 2442 MHz [7] (22.0 dBm)
			* 2447 MHz [8] (22.0 dBm)
			* 2452 MHz [9] (22.0 dBm)
			* 2457 MHz [10] (22.0 dBm)
			* 2462 MHz [11] (22.0 dBm)
			* 2467 MHz [12] (disabled)
			* 2472 MHz [13] (disabled)
	Band 2:
		Capabilities: 0x11ee
			HT20/HT40
			SM Power Save disabled
			RX HT20 SGI
			RX HT40 SGI
			TX STBC
			RX STBC 1-stream
			Max AMSDU length: 3839 bytes
			DSSS/CCK HT40
		Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
		Minimum RX AMPDU time spacing: 4 usec (0x05)
		HT Max RX data rate: 300 Mbps
		HT TX/RX MCS rate indexes supported: 0-15
		VHT Capabilities (0x038071a0):
			Max MPDU length: 3895
			Supported Channel Width: neither 160 nor 80+80
			short GI (80 MHz)
			TX STBC
			SU Beamformee
		VHT RX MCS set:
			1 streams: MCS 0-9
			2 streams: MCS 0-9
			3 streams: not supported
			4 streams: not supported
			5 streams: not supported
			6 streams: not supported
			7 streams: not supported
			8 streams: not supported
		VHT RX highest supported: 0 Mbps
		VHT TX MCS set:
			1 streams: MCS 0-9
			2 streams: MCS 0-9
			3 streams: not supported
			4 streams: not supported
			5 streams: not supported
			6 streams: not supported
			7 streams: not supported
			8 streams: not supported
		VHT TX highest supported: 0 Mbps
		Bitrates (non-HT):
			* 6.0 Mbps
			* 9.0 Mbps
			* 12.0 Mbps
			* 18.0 Mbps
			* 24.0 Mbps
			* 36.0 Mbps
			* 48.0 Mbps
			* 54.0 Mbps
		Frequencies:
			* 5180 MHz [36] (22.0 dBm) (no IR)
			* 5200 MHz [40] (22.0 dBm) (no IR)
			* 5220 MHz [44] (22.0 dBm) (no IR)
			* 5240 MHz [48] (22.0 dBm) (no IR)
			* 5260 MHz [52] (22.0 dBm) (no IR, radar detection)
			* 5280 MHz [56] (22.0 dBm) (no IR, radar detection)
			* 5300 MHz [60] (22.0 dBm) (no IR, radar detection)
			* 5320 MHz [64] (22.0 dBm) (no IR, radar detection)
			* 5500 MHz [100] (22.0 dBm) (no IR, radar detection)
			* 5520 MHz [104] (22.0 dBm) (no IR, radar detection)
			* 5540 MHz [108] (22.0 dBm) (no IR, radar detection)
			* 5560 MHz [112] (22.0 dBm) (no IR, radar detection)
			* 5580 MHz [116] (22.0 dBm) (no IR, radar detection)
			* 5600 MHz [120] (22.0 dBm) (no IR, radar detection)
			* 5620 MHz [124] (22.0 dBm) (no IR, radar detection)
			* 5640 MHz [128] (22.0 dBm) (no IR, radar detection)
			* 5660 MHz [132] (22.0 dBm) (no IR, radar detection)
			* 5680 MHz [136] (22.0 dBm) (no IR, radar detection)
			* 5700 MHz [140] (22.0 dBm) (no IR, radar detection)
			* 5720 MHz [144] (22.0 dBm) (no IR, radar detection)
			* 5745 MHz [149] (22.0 dBm) (no IR)
			* 5765 MHz [153] (22.0 dBm) (no IR)
			* 5785 MHz [157] (22.0 dBm) (no IR)
			* 5805 MHz [161] (22.0 dBm) (no IR)
			* 5825 MHz [165] (22.0 dBm) (no IR)
	Supported commands:
		 * new_interface
		 * set_interface
		 * new_key
		 * start_ap
		 * new_station
		 * new_mpath
		 * set_mesh_config
		 * set_bss
		 * authenticate
		 * associate
		 * deauthenticate
		 * disassociate
		 * join_ibss
		 * join_mesh
		 * remain_on_channel
		 * set_tx_bitrate_mask
		 * frame
		 * frame_wait_cancel
		 * set_wiphy_netns
		 * set_channel
		 * set_wds_peer
		 * start_sched_scan
		 * probe_client
		 * set_noack_map
		 * register_beacons
		 * start_p2p_device
		 * set_mcast_rate
		 * connect
		 * disconnect
		 * channel_switch
		 * set_qos_map
		 * add_tx_ts
		 * Unknown command (121)
	Supported TX frame types:
		 * IBSS: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
		 * managed: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
		 * AP: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
		 * AP/VLAN: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
		 * mesh point: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
		 * P2P-client: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
		 * P2P-GO: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
		 * P2P-device: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
	Supported RX frame types:
		 * IBSS: 0x40 0xb0 0xc0 0xd0
		 * managed: 0x40 0xd0
		 * AP: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
		 * AP/VLAN: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
		 * mesh point: 0xb0 0xc0 0xd0
		 * P2P-client: 0x40 0xd0
		 * P2P-GO: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
		 * P2P-device: 0x40 0xd0
	WoWLAN support:
		 * wake up on disconnect
		 * wake up on magic packet
		 * wake up on pattern match, up to 20 patterns of 16-128 bytes,
		   maximum packet offset 0 bytes
		 * can do GTK rekeying
		 * wake up on GTK rekey failure
		 * wake up on EAP identity request
		 * wake up on 4-way handshake
		 * wake up on rfkill release
		 * wake up on network detection, up to 11 match sets
		 * wake up on TCP connection
	software interface modes (can always be added):
		 * AP/VLAN
		 * monitor
	valid interface combinations:
		 * #{ managed } <= 1, #{ AP, P2P-client, P2P-GO } <= 1, #{ P2P-device } <= 1,
		   total <= 3, #channels <= 2
	HT Capability overrides:
		 * MCS: ff ff ff ff ff ff ff ff ff ff
		 * maximum A-MSDU length
		 * supported channel width
		 * short GI for 40 MHz
		 * max A-MPDU length exponent
		 * min MPDU start spacing
	Device supports TX status socket option.
	Device supports HT-IBSS.
	Device supports SAE with AUTHENTICATE command
	Device supports low priority scan.
	Device supports scan flush.
	Device supports per-vif TX power setting
	P2P GO supports CT window setting
	P2P GO supports opportunistic powersave setting
	Driver supports full state transitions for AP/GO clients
	Driver supports a userspace MPM
	Driver/device bandwidth changes during BSS lifetime (AP/GO mode)
	Device supports static SMPS
	Device supports dynamic SMPS
	Device supports WMM-AC admission (TSPECs)
	Device supports configuring vdev MAC-addr on create.

iw reg get showing reg domain set to US:

$ iw reg get
global
country US: DFS-FCC
	(2402 - 2472 @ 40), (N/A, 30), (N/A)
	(5170 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
	(5250 - 5330 @ 80), (N/A, 23), (0 ms), DFS, AUTO-BW
	(5490 - 5730 @ 160), (N/A, 23), (0 ms), DFS
	(5735 - 5835 @ 80), (N/A, 30), (N/A)
	(57240 - 63720 @ 2160), (N/A, 40), (N/A)

iw scan output, also showing HT20/HT40 capability for 40 MHz channel width:

$ sudo iw dev wlan0 scan | head -100
BSS 10:xx:xx:xx:xx:9d(on wlan0) -- associated
	last seen: 3761.655s [boottime]
	TSF: 3659297206 usec (0d, 01:00:59)
	freq: 5805
	beacon interval: 100 TUs
	capability: ESS Privacy (0x0011)
	signal: -65.00 dBm
	last seen: 156 ms ago
	Information elements from Probe Response frame:
	SSID: xxx-n
	Supported rates: 6.0* 9.0 12.0* 18.0 24.0* 36.0 48.0 54.0 
	DS Parameter set: channel 161
	RSN:	 * Version: 1
		 * Group cipher: CCMP
		 * Pairwise ciphers: CCMP
		 * Authentication suites: PSK
		 * Capabilities: 16-PTKSA-RC 1-GTKSA-RC (0x000c)
	HT capabilities:
		Capabilities: 0x11ef
			RX LDPC
			HT20/HT40
			SM Power Save disabled
			RX HT20 SGI
			RX HT40 SGI
			TX STBC
			RX STBC 1-stream
			Max AMSDU length: 3839 bytes
			DSSS/CCK HT40
		Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
		Minimum RX AMPDU time spacing: 8 usec (0x06)
		HT TX/RX MCS rate indexes supported: 0-23
	HT operation:
		 * primary channel: 161
		 * secondary channel offset: above
		 * STA channel width: any
		 * RIFS: 0
		 * HT protection: 20 MHz
		 * non-GF present: 1
		 * OBSS non-GF present: 0
		 * dual beacon: 0
		 * dual CTS protection: 0
		 * STBC beacon: 0
		 * L-SIG TXOP Prot: 0
		 * PCO active: 0
		 * PCO phase: 0
	Extended capabilities: 6
	WMM:	 * Parameter version 1
		 * BE: CW 15-1023, AIFSN 3, TXOP 2048 usec
		 * BK: CW 15-1023, AIFSN 7
		 * VI: CW 7-15, AIFSN 2, TXOP 3008 usec
		 * VO: CW 3-7, AIFSN 2, TXOP 1504 usec

Last edited by alex.forencich (2017-09-25 22:48:04)

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#2 2017-09-25 08:05:31

seth
Member
Registered: 2012-09-03
Posts: 59,040

Re: [SOLVED] Why is my wifi getting downgraded to 20 MHz channel width?

channel 161 (5805 MHz), width: 20 MHz, center1: 5805 MHz

I'm not firm with actual national regulations on this, but wikipedia lists the frequency w/ only 20Hz - https://en.wikipedia.org/wiki/List_of_W … Fn.2Fac.29

So you got to pick another channel.

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#3 2017-09-25 17:54:17

alex.forencich
Member
Registered: 2011-05-29
Posts: 96

Re: [SOLVED] Why is my wifi getting downgraded to 20 MHz channel width?

This was actually a dd-wrt auto-selected channel, and a OnePlus 3T phone successfully connected at HT40. 

I can't select any of the 40 MHz and 80 MHz marked channels on the router.  The channel list seems to go up mostly by 4s - 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144, 149, 153, 157, 161, 165.  However, the way HT40 works is by bonding two adjacent 20 MHz channels...so a channel made from 161 and 165 would actually be centered at 163, which is interestingly missing from that table.  That may be the key here. 

Trying 140/144 seems to work, with the center at 142, which is in the table, and marked as a 40 MHz channel:

$ iw dev
phy#0
	Interface wlan0
		ifindex 4
		wdev 0x1
		addr e8:xx:xx:xx:xx:13
		ssid banana-n
		type managed
		channel 140 (5700 MHz), width: 40 MHz, center1: 5710 MHz
		txpower 22.00 dBm

Seems like channel 36/40 (centered on 38) also works:

$ iw dev
phy#0
	Interface wlan0
		ifindex 4
		wdev 0x1
		addr e8:xx:xx:xx:xx:13
		ssid banana-n
		type managed
		channel 36 (5180 MHz), width: 40 MHz, center1: 5190 MHz
		txpower 22.00 dBm

Seems like channel 163 is supposed to be a 160 MHz channel...which would run off the end of the band.  However, it seems like running it at 40 MHz should, in theory, be fine.  https://www.rsm.govt.nz/consumers/pdf-a … 20Band.pdf

Seems like the lesson here is that auto channel selection in dd-wrt doesn't work right with 40 MHz channels, and apparently you can't pick any random pair of adjacent 20 MHz channels to make a 40 MHz channel.

Last edited by alex.forencich (2017-09-25 17:55:35)

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