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Re: Can Anyone Explain the over-all view of Wireless Networking?



On Wed, Feb 03, 2010 at 12:44:45AM -0600, Kent West wrote:
> Celejar wrote:
> > This is the networking subsystem attempting to configure the wireless
> > interface.
> >
> >   
> >> Sending on   LPF/wlan0/00:18:f8:29:b5:96
> >> Sending on   Socket/fallback
> >> DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 4
> >> DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 11
> >> DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 11
> >> DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 10
> >> DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 13
> >> DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 7
> >> DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 5
> >> No DHCPOFFERS received.
> >> No working leases in persistent database - sleeping.
> >> done.
> >>     
> >
> > It is failing.  Now, IME, most such failures are due to the card not
> > being properly associated with the AP.  You can determine this by
> > either looking at syslog, or by calling 'iwconfig wlan0'.  If it's
> > properly associated, the first two lines should be something like this:
> >
> > wlan0     IEEE 802.11bg  ESSID:"nnnnnnn"  
> >           Mode:Managed  Frequency:2.437 GHz  Access Point: 12:34:56:78:99:aa
> >
> > If it's not, you'll see something like this:
> >
> > wlan0     IEEE 802.11bg  ESSID:off/any  
> >           Mode:Managed  Access Point: Not-Associated
> >
> > Information in syslog will be helpful in determining the cause of failure.
> >   
> Stuff like this in dmesg:
> 
> status=10 aid=0)
> [  575.125696] wlan0: AP denied association (code=10)
> [  575.321089] wlan0: association with AP 00:0b:86:bb:83:40 timed out
> [  594.893308] wlan0: deauthenticated (Reason: 1)
> [  652.178643] wlan0: direct probe to AP 00:0b:86:bb:83:40 try 1
> 

I have seen this exact behavior at my uni. The wireless tools are
picking, generally, the AP with the strongest signal and trying to
associate with it. But that AP denies association for whatever reason
(too busy perhaps), but the tools aren't smart enough to realize this
and move on to the next AP and try associating. 

My solution, for quite a while, was repeated issuances of:

sudo iwconfig wlan0 ap off

while watching a syslog tail. Then I would see it finally associate
and *hopefully* do it before dhclient times out. 

In my experience, this means that your wireless is essentially working
correctly, but is just not getting association with a free AP. Around
my school, this behavior is correlated with the number of running
laptops in the vicinity. For example, over in the liberal arts areas,
there are relatively few laptops and the AP's are generally
available. I can associate on the first or second try. Meanwhile in
the CS and engineering areas, laptops proliferate like bunnies and it
can take several attempts to get association. 


[...]

> I thought I was through with the machine, but I may have to bring it
> back up to the ACUWireless network, so I might get to play with it some
> more. 

I finally installed wicd and it is sophisticated enough to handle this
situation. Now my wireless just works. It can be slow to come alive if
there is a lot of traffic around, but it still gets me connected with
no fiddling on my part. 

very much my .02

A

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