From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vk0-x229.google.com (mail-vk0-x229.google.com [IPv6:2607:f8b0:400c:c05::229]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 374FB3B25D; Fri, 13 May 2016 23:19:01 -0400 (EDT) Received: by mail-vk0-x229.google.com with SMTP id c189so5927147vkb.1; Fri, 13 May 2016 20:19:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc; bh=4Y6RUEuDd5DdnITONVOOqN5p8OXj/g1My/Gq+3ii58Y=; b=fpACGNp4tm5T0TClxRgJwVj0cLH/Kge/KZXin+lKTak7WxEL2LaygdPjiRWQK6ZH8L w46qeShj41LG84KUYTPRaGyR9zvO2+5TbIJ6dlFTjj6SA2n74eDkA16jchZe2JaoKQso dpBUX+ApLoio0YlRWv3rQ4Sa6oQUu9JxXLjyLtcKw3jMiuUG8v/DwctJksapgJW4SPx1 ynRvC8mVdbtn39SbWmzAh+jVZv/xo60LWMGjHduGv3k+z8qe3vJoJ/p9ll8JjkMWZ50C Vic3oa9RpSPzSPdVXkdnrzfc8MEzKjy9lDS+cRnFtcSZU2R3GGlpfaZd4gKVBzxWgW9p vAMQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc; bh=4Y6RUEuDd5DdnITONVOOqN5p8OXj/g1My/Gq+3ii58Y=; b=fn4ebtIusOP9WApgnOiN8+E4qAxPWfwtJ+teazSprfcaaZd2hAJaixbobfUSvStoYV 3H88hlp5knpQJDU93sVPUBkUp50HIRnQr7DTq2qoBnGm58MMfHh9cUe+F536KAqSomvo n5JEWFeNGyMKtZRDJoueMlQZ+jQ2+HTzyZ/LNjkJONxe9ZU3u12VC07i0HcbUkkMcMb9 eu0MuwG/lq3yYaFyS/PTADovCauz9mCOMla+Xbk251qhUFpYPvWJCPL91wfCtVBc7ItE fop7lbf7hu00uMYMpIrOsKhcoeDSKHwyzKszdcoKP9ANNmSyim60ez5MEqZGYV85MgMZ bEVA== X-Gm-Message-State: AOPr4FVsAK/39L0tOtVdR4FlmwvKzDjpg/2DMQaEaYHpCxThmijnvyudXfRXvlP8C9FOiKUXQ3ihuEZFg83LwA== MIME-Version: 1.0 X-Received: by 10.176.4.20 with SMTP id 20mr9301961uav.125.1463195940795; Fri, 13 May 2016 20:19:00 -0700 (PDT) Received: by 10.103.44.70 with HTTP; Fri, 13 May 2016 20:19:00 -0700 (PDT) In-Reply-To: References: Date: Fri, 13 May 2016 20:19:00 -0700 Message-ID: From: Aaron Wood To: Dave Taht Cc: make-wifi-fast@lists.bufferbloat.net, "cerowrt-devel@lists.bufferbloat.net" Content-Type: multipart/alternative; boundary=001a114fd88649c1250532c4daab Subject: Re: [Make-wifi-fast] what is the right way to do, and rationale, for wifi channel scans? X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 14 May 2016 03:19:01 -0000 --001a114fd88649c1250532c4daab Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable wpa_supplicant? I've seen some atrocious behavior from wpa_supplicant in the past (especially the closed-source versions from some chipset companies). One reason it's likely to be scanning is that it's looking for alternate APs for the same SSID, which are "better". I saw one implementation that would do an all-channel wildcard ssid scan (elicting a response from every AP in range), and then would proceed to scan every channel for just the ssid it was configured to use (hardcoded in the wifi config). Why it was doing a broadcast for all APs, I don't know. But once you get enough APs in a small enough area, that behavior causes a broadcast storm as the probe responses (all at 1Mbps) flood the air, and then cause other STAs to miss beacons, and re-scan, and it death-spirals from there. -Aaron On Fri, May 13, 2016 at 5:19 PM, Dave Taht wrote: > I finally tracked down the source of many of the anomalies I'd > seen thus far... channel scans. > > For the related rant, see: > > http://blog.cerowrt.org/post/disabling_channel_scans/ > > Still haven't been able to kill it off entirely. > > -- > Dave T=C3=A4ht > Let's go make home routers and wifi faster! With better software! > http://blog.cerowrt.org > _______________________________________________ > Make-wifi-fast mailing list > Make-wifi-fast@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/make-wifi-fast > --001a114fd88649c1250532c4daab Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
wpa_supplicant?=C2=A0 I've seen some atrocious behavio= r from wpa_supplicant in the past (especially the closed-source versions fr= om some chipset companies).

One reason it's likely t= o be scanning is that it's looking for alternate APs for the same SSID,= which are "better".

I saw one implement= ation that would do an all-channel wildcard ssid scan (elicting a response = from every AP in range), and then would proceed to scan every channel for j= ust the ssid it was configured to use (hardcoded in the wifi config).=C2=A0= Why it was doing a broadcast for all APs, I don't know.=C2=A0 But once= you get enough APs in a small enough area, that behavior causes a broadcas= t storm as the probe responses (all at 1Mbps) flood the air, and then cause= other STAs to miss beacons, and re-scan, and it death-spirals from there.<= /div>

-Aaron

<= div class=3D"gmail_quote">On Fri, May 13, 2016 at 5:19 PM, Dave Taht <da= ve.taht@gmail.com> wrote:
I= finally tracked down the source of many of the anomalies I'd
seen thus far... channel scans.

For the related rant, see:

http://blog.cerowrt.org/post/disabling_channel_= scans/

Still haven't been able to kill it off entirely.

--
Dave T=C3=A4ht
Let's go make home routers and wifi faster! With better software!
ht= tp://blog.cerowrt.org
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Make-wifi-fast mailing list
Make-wifi-fast@list= s.bufferbloat.net
https://lists.bufferbloat.net/listinfo/make-wif= i-fast

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