Re: connection lost on roaming wifi networks



On Mon, 2010-09-20 at 11:24 +0200, Jirka Klimes wrote:
> On Monday 20 of September 2010 09:36:27 Frederik Himpe wrote:
> > On Fri, 17 Sep 2010 10:55:23 +0200, Jirka Klimes wrote:
> > > On Wednesday 15 of September 2010 14:52:02 Frederik Himpe wrote:
> > >> I'm using Debian Squeeze kernel 2.6.32-21 (iwlagn 1.3.27ks) with an
> > >> Intel Corporation Ultimate N WiFi Link 5300 [8086:4235].
> > >> 
> > >> Whenever I use my laptop in a place where different APs provide roaming
> > >> for a wifi network, my system seems to suddenly (without moving) roam
> > >> to another AP, after which the connection stops working completely
> > >> (cannot ping anymore, etc) while NetworkManager shows I'm still
> > >> connected.
> > >> 
> > >> I can easily reproduce this, on two different roaming networks.
> > >> 
> > >> I also tried kernel 2.6.35-1~experimental.3, but it has the same
> > >> problematic behaviour.
> > > 
> > > There's a problem with getting IP from DHCP server. See DHCPREQUEST
> > > requests, but no reply. Is the DHCP server properly running, replying?
> > > Try to capture packets in wireshark to see if there is any DHCP server
> > > response.
> > > Or just configure the connection with static IP to verify that the
> > > issues are indeed due to DHCP.
> > 
> > No, the issue is not DHCP: the fact that there is no reply to the
> > DHCPREQUEST is just a symptom of my problem, but it is not the cause. The
> > problem already starts from Sep 14 09:14:43, when it decides to roam.
> > From that moment on, the connection is broken. A few minutes later, when
> > my old DHCP lease expires, and then it fails to get a new one because the
> > wifi connection is broken.
> 
> The issue can be caused by a number of things. DHCP was just a guess from the 
> logs you've provided.
> Try to collect and analyze more logs to find the real issue.
> One cause of the problem could be the iwlagn driver. Is anything interesting 
> in dmesg? Try removing and inserting the driver: rmmod iwlagn; modprobe iwlagn
> You can also disable "n" band using driver options: see 
> https://bugzilla.redhat.com/show_bug.cgi?id=587825#c8
> 
> What about wpa_supplicant logs?

Supplicant logs would be quite necessary to figure out what's going on.
But you're entirely right... it could be wpa_supplicant, the driver
itself, the wifi card firmware, or mac80211.  It's highly unlikely that
it's NM itself, because NM is not actually much involved in intra-ESS
roaming.  That's all the driver and wpa_supplicant.

Dan




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