On 08/30/18 at 08:55am, Luca Coelho wrote:

On Thu, 2018-08-30 at 13:06 +0800, Dave Young wrote:

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On 08/30/18 at 07:15am, Luca Coelho wrote:

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On Wed, 2018-08-29 at 14:54 +0800, Dave Young wrote:

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[   74.123114] wlp61s0: authenticate with 00:1f:c6:82:0a:57
[   74.126099] wlp61s0: send auth to 00:1f:c6:82:0a:57 (try 1/3)
[   74.139740] wlp61s0: authenticated
[   74.140142] iwlwifi 0000:3d:00.0 wlp61s0: disabling HE/HT/VHT due to WEP/TKIP use
[   74.140146] iwlwifi 0000:3d:00.0 wlp61s0: disabling HT as WMM/QoS is not supported by the AP
[   74.140149] iwlwifi 0000:3d:00.0 wlp61s0: disabling VHT as WMM/QoS is not supported by the AP

Your AP seems to be configured to use WEP or TKIP, which is not allowed
by IEEE802.11n, so we disable all the higher rates, as you can see
here.  It should still work, but you will only get very basic rates
(i.e. slow).

Luka, thanks for the suggestion,  moved AP to use WPA2-personal + AES.
seems I got only two features disabled this time:
[   20.949347] iwlwifi 0000:3d:00.0 wlp61s0: disabling HT as WMM/QoS is not supported by the AP
[   20.949351] iwlwifi 0000:3d:00.0 wlp61s0: disabling VHT as WMM/QoS is not supported by the AP
[   20.949622] wlp61s0: associate with 00:1f:c6:82:0a:57 (try 1/3)

There are many interoperability problems with old 11n APs that either
support a draft version of the specs or simply have bugs in their
implementations of the 11n specs.  When we detect these problems, we
disable 11n rates, so connectivity will be slower, but it will at least
remain connected.  This seems to be the case with your AP. :(

This seems not cause much slower connection.
But WMM indeed cause a very slow connection, thus I just leave WMM
disabled as before.

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[ 2521.068469] wlp61s0: deauthenticating from 00:1f:c6:82:0a:57 by local choice (Reason: 3=DEAUTH_LEAVING)

Other than that I can't really see what is going on, except that
something is deciding to disconnect here...

So, first thing I'd suggest would be to try to reconfigure your AP to
use something else than WEP or TKIP, just to see if it improves in any
way.

Will observe if it works or not. BTW, my old laptop Thinkpad T440s works
well with the same AP.

I hope it improves.  If not, we should debug it further.  It's a good
thing not to use WEP and TKIP anyway, because they're not very secure
anyway.

Ok, will provide feedback later, thanks!

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And BTW, is this a regression in recent kernels or has this always
happened to you with this laptop/AP combination?

From my observation it just always happen, but hmm not 100% sure..

Okay, so we don't have enough information on this.  It doesn't matter. 
What is the NIC on your old T440s?

It is Intel wireless 7260, but since the laptop is not at hand I can not
get lspci details.

--
Cheers,
Luca.

Thanks
Dave