16.04: issues with wireless on MacBook Pro

Paul Smith paul at mad-scientist.net
Sun Jul 3 20:50:44 UTC 2016

On Fri, 2016-07-01 at 07:28 +0200, Nils Kassube wrote:
> > If I run iwevent I can see a message "Scan request completed" exactly
> > every 2 minutes.  I don't know if that's normal or not.  No other
> > messages are shown.  dmesg shows no messages since I booted.
> That looks to me like network manager scans for other networks every two 
> minutes. As you have an a/b/g/n wireless card, it will scan all 
> available channels on the 2 GHz and on the 5 GHz bands which takes quite 
> some time. On my machine with an a/b/g/n card a scan takes ~14 seconds 
> with only 4 access points visible. And during this time it doesn't 
> transfer the data you're intersted in.
> That was the reason why I abandoned network manager many years ago - 
> especially video chat with ekiga was unacceptable with regular sound 
> drops. Since then I use wicd on all machines and never had such a 
> problem again.

Thanks for this note.  It put me on the right track, and I was able to
find a solution using Network Manager.  Apparently if you configure the
wireless connection with the specific MAC address of your wireless
access point in the BSSID field, then Network Manager won't look for
"better" connections.

To do this open the Network applet, select Wi-Fi, choose the gear config
button on the wireless connection, then under Identity choose the drop-
down next to BSSID; most likely it will have just a single MAC address
in it unless you're in some kind of corporate environment: select that
and hit Apply.

I still see the scan requests going by every 2 minutes but it doesn't
seem to interrupt my network access.  I would like an option to force
scanning off altogether: 99.9% of the time when I use my laptop I
actually _don't_ want to roam and I know exactly which network I want to
connect to.  But, as long as it doesn't interrupt my work it doesn't
bother me much.  It appears this is something of a contentious issue in
the Network Manager world, unfortunately.  The author(s) refuse to allow
this configuration option and insist that if wifi drivers were written
correctly it would not be necessary.  However this doesn't help people
like me who have no choice (company-provided hardware) but to use
proprietary wireless drivers which apparently aren't written correctly.

I want to use Network Manager because (a) it's built in and easy, and
(b) I need to use various VPNs, and wicd (from what I can tell) doesn't
support this yet.


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