Intel Wireless broken on Ubuntu 9.04

2009-12-21: Update - Working just fine with Ubuntu 9.10 !!

After using the Auto Update on Ubuntu 9.04 recently, the Intel wireless in my laptop stopped working. More exactly, it would associate to the same-old AP configured in the Network Connections applet, but after 20-30 seconds trying to authenticate it would fail.

The output of sudo dmesg would be along these lines:

[ 1494.509061] wlan0: authenticate with AP 00:1d:68:0a:fb:11
[ 1494.511257] wlan0: authenticated
[ 1494.511264] wlan0: associate with AP 00:1d:68:0a:fb:11
[ 1494.513984] wlan0: RX ReassocResp from 00:1d:68:0a:fb:11 (capab=0x11 status=0 aid=2)
[ 1494.513990] wlan0: associated
[ 1540.343855] wlan0: disassociating by local choice (reason=3)

This is with using
- an Intel 4965AGN (dmesg reports as 'Intel Wireless WiFi Link 4965AGN REV=0x4')
- a single Access Point requiring WPA/WPA2 in 802.11 mixed b/g mode

After some searching, it seems that a recent update to the iwlagn driver has trouble selecting the rate or authentication (or talking to WPA_supplicant). One suggestion found, which works for is to do the following:

# sudo modprobe -r iwlagn
# sudo modprobe iwlagn 11n_disable=1 11n_disable50=1

This first unloads the module, then re-loads it with 11n disabled in both the 2.4GHz band (11n_disable=1) and the 5.0Ghz band (11n_disable50=1).

The connection manager then immediately retried and connected....

(The 'offending' driver appears to be Intel(R) Wireless WiFi Link AGN driver for Linux, 1.3.27ks)