Very unstable wifi connection after upgrade to 12.04 (Intel Ultimate-N 6300)

Hello,

after dist-upgrade from 11.10 to 12.04 (64bit), my wifi connection got very unstable, and keeps bugging me. Until the dist-upgrade, everything worked fine. My hardware is a ThinkPad T420 with a Intel Ultimate-N 630 wireless network controller.

In short words, the connection stops working at some random point, and I didn't figure out why yet. Unfortunately no log message seems to be printed to any log file at the time of lost connection. NetworkManager keeps telling me that the connection is alive, but neither ping to the router/switch nor DNS-lookup work anymore. Ifconfig still lists the IP-address, and iwconfig doesn't show anything suspicious either.

Nobody else in the same Wifi-network has similar problems - even though I've to admit that nobody else uses Ubuntu here.

I already searched the forum. Some people seem to discover similar issues after upgrade to Ubuntu 12.04, though I'm not sure whether they're the same - at least it's on different hardware:
http://ubuntuforums.org/showthread.php?t=1975442
http://ubuntuforums.org/showthread.php?t=1958059

Unfortunately I don't have any idea about how to futher debug this problem. As one can imagine, it's very annoying. After all it randomly breaks my network/internet connection. Any help is much appreciates :)

Regards,
jonas

Below follows some information about WLAN and hardware. No differences between working and non-working WLAN-connection.

Code:

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$ lspci -v -s 03:00.0
03:00.0 Network controller: Intel Corporation Centrino Ultimate-N 6300 (rev 35)
    Subsystem: Intel Corporation Centrino Ultimate-N 6300 3x3 AGN
    Flags: bus master, fast devsel, latency 0, IRQ 46
    Memory at f2500000 (64-bit, non-prefetchable) [size=8K]
    Capabilities: <access denied>
    Kernel driver in use: iwlwifi
    Kernel modules: iwlwifi

---

Code:

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$ ifconfig wlan0
wlan0    Link encap:Ethernet  HWaddr **:**:**:**:**:**
          inet addr:192.168.0.103  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: ****::****:****:****:****/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:74576 errors:0 dropped:0 overruns:0 frame:0
          TX packets:60632 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:65942630 (65.9 MB)  TX bytes:8546658 (8.5 MB)

---

Code:

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$ iwconfig wlan0
wlan0    IEEE 802.11abgn  ESSID:"**********"
          Mode:Managed  Frequency:2.437 GHz  Access Point: **:**:**:**:**:**
          Bit Rate=57.8 Mb/s  Tx-Power=15 dBm
          Retry  long limit:7  RTS thr:off  Fragment thr:off
          Power Management:off
          Link Quality=47/70  Signal level=-63 dBm
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:9248  Invalid misc:57  Missed beacon:0

---

Please try a driver parameter:

Code:

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sudo modprobe -r iwlwifi
sudo modprobe iwlwifi 11n_disable=1

---

Does stability improve? If so, we can write a quick file and make it persistent.

Thanks for the hint. It seems to do the rick.

I guess that you're refering to a issue with iwlwifi in kernel 3.2 discussed here: https://bugzilla.redhat.com/show_bug.cgi?id=785239

I added the option '11n_disable=1' for module iwlwifi in /etc/modprobe.d. Since this change, I didn't discover unstable/broken wifi connection issues so far.

Quote:

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I guess that you're refering to a issue with iwlwifi in kernel 3.2 discussed here: https://bugzilla.redhat.com/show_bug.cgi?id=785239

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.ko-rrect. A little insiders driver joke there. The bug has lasted longer than kernel 3.2xx; it also affected the predecessor iwlagn and 3.0xx. I wish Intel would crack this case; N is here to stay.

If you please, use thread tools at the top to Mark Solved. The searchers will appreciate it.

Quote:

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Originally Posted by chili555

If you please, use thread tools at the top to Mark Solved. The searchers will appreciate it.

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Sure, will do this. But first, I'll wait a few more days and see whether the wifi issues really disappeared. Thanks again for your help.

Quote:

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Originally Posted by mejo

Sure, will do this. But first, I'll wait a few more days and see whether the wifi issues really disappeared. Thanks again for your help.

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After two days with the new module parameter, no wifi connection problems any longer. Marking the problem as solved.

Quote:

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Originally Posted by chili555

Please try a driver parameter:

Code:

---

sudo modprobe -r iwlwifi
sudo modprobe iwlwifi 11n_disable=1

---

Does stability improve? If so, we can write a quick file and make it persistent.

---

This worked for me. Thanks!

This is a workaround, but not a true solution to the underlying problem. Still, having a reliable connection (even at a slower speed) is much better than a flaky connection (or no connection at all).

Just a note to say that the problem can be reproduced still today with latest Ubuntu stable and a Thinkpad T430, also with Intel Corporation Centrino Ultimate-N 6300 (rev 3e)

The bug report to watch and vote seems to be

[Oneiric] [Regression] Intel Corporation Centrino Ultimate-N 6300 poor networking, packet loss and very slow Lenovo X201 and T500 laptops
https://bugs.launchpad.net/ubuntu/+s...ux/+bug/836250

And the ultimate source:

http://bugzilla.intellinuxwireless.o...ug.cgi?id=2315

Quote:

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Originally Posted by chili555

Please try a driver parameter:

Code:

---

sudo modprobe -r iwlwifi
sudo modprobe iwlwifi 11n_disable=1

---

Does stability improve? If so, we can write a quick file and make it persistent.

---

I have the same problem, tried the two sudo and they did not help.

I also tried to add "the option '11n_disable=1' for module iwlwifi in /etc/modprobe.d.", but I don't even find the file, here is ls:

-rw-r--r-- 1 root root 2507 Feb 15 2012 alsa-base.conf
-rw-r--r-- 1 root root 325 Apr 13 2010 blacklist-ath_pci.conf
-rw-r--r-- 1 root root 1603 Apr 13 2010 blacklist.conf
-rw-r--r-- 1 root root 210 Mar 18 2011 blacklist-firewire.conf
-rw-r--r-- 1 root root 661 Nov 20 2011 blacklist-framebuffer.conf
-rw-r--r-- 1 root root 156 Jan 28 2010 blacklist-modem.conf
lrwxrwxrwx 1 root root 41 Nov 13 11:25 blacklist-oss.conf -> /lib/linux-sound-base/noOSS.modprobe.conf
-rw-r--r-- 1 root root 583 Mar 18 2011 blacklist-rare-network.conf
-rw-r--r-- 1 root root 1077 Apr 13 2010 blacklist-watchdog.conf
-rw-r--r-- 1 root root 127 Apr 22 2012 dkms.conf
-rw-r--r-- 1 root root 16 Jan 6 2010 libpisock9.conf
-rw-r--r-- 1 root root 30 May 18 2012 vmwgfx-fbdev.conf

could anyone help me? Do I need to check my hardware? better if I could just change config files...