Installation

1) Install linux image 2.6.23 or above 2.6.24 The iwl* modules requires the new kernel's IEEE 802.11 subsystem (mac80211). both modules are available in linux-image-2.6.24 (currently in DebianUnstable).

2) Install firmware-iwlwifi

It's assumed you know how to install both!?

Loading the iwl3945 / iwl4965 modules

The module should be loaded automatically by udev when the system starts.

Using iwlWifi

use network-manager to use the interface !
Alternatively, for those who prefer using ifup/ifdown from the command line, I used the following stanza in /etc/network/interfaces/:

iface wlan0 inet dhcp
  pre-up ip link set wlan0 up
  wireless_essid MakeTeaNotWar

Note the magic pre-up line, which I needed to make the card associate with the access point. As a bonus, with this stanza the interface works after an S3 resume (i.e. suspend/resume to RAM)!

Interfaces

Once the module is loaded, ip a should show two interfaces (wlan0 is the "main" one).

3: wmaster0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc ieee80211 qlen 1000
    link/ieee802.11 00:13:e8:70:69:fb brd ff:ff:ff:ff:ff:ff
4: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:13:e8:70:69:fb brd ff:ff:ff:ff:ff:ff

Switching from ipw3945 to iwl3945

Install as explained above.
Check for the line generated by udev for ipw3945 in /etc/udev/rules.d/z25_persistent-net.rules. If it is there, remove it (more explanation in "Common problems and errors" below).
Optionally, change the configuration in /etc/network/interfaces by replacing eth2 (or whatever the old name for wireless interface is) with wlan0.
Reboot into the new kernel.
Verify that wireless networking is functional.
Remove the ipw3945-modules-* and ipw3945d packages.

Common problems and errors

Interfaces is named "wlan0_rename" (sysfs_create_symlink failed)

Another symptom is that Network-manager don't handle the wireless card.

/var/log/syslog may show :

kernel: iwl3945: Intel(R) PRO/Wireless 3945ABG/BG Network Connection driver for Linux, 0.1.15ks
kernel: iwl3945: Copyright(c) 2003-2007 Intel Corporation
kernel: ACPI: PCI Interrupt 0000:03:00.0[A] -> GSI 17 (level, low) -> IRQ 22
kernel: PCI: Setting latency timer of device 0000:03:00.0 to 64
kernel: iwl3945: Detected Intel PRO/Wireless 3945ABG Network Connection
kernel: iwl3945: Tunable channels: 13 802.11bg, 23 802.11a channels
kernel: wmaster0: Selected rate control algorithm 'iwl-3945-rs'
kernel: net eth2: device_rename: sysfs_create_symlink failed (-17)
kernel: udev: renamed network interface wmaster0 to eth2
kernel: net wlan0_rename: device_rename: sysfs_create_symlink failed (-17)

This may occur if you had used ipw3945 module before.

Resolution

in /etc/udev/rules.d/z25_persistent-net.rules remove the line like

# PCI device 0x8086:0x4227 (ipw3945)
SUBSYSTEM=="net", DRIVERS=="?*", ATTRS{address}=="00:13:02:4c:12:12", NAME="eth2"

then remove the module and re-insert it.

rmmod iwl3945
modprobe iwl3945

in /etc/udev/rules.d/z25_persistent-net.rules you should now have a line like :

# PCI device 0x8086:0x4227 (iwl3945)
SUBSYSTEM=="net", DRIVERS=="?*", ATTR{address}=="00:13:02:4c:12:12", ATTR{type}=="1", NAME="wlan0"

Card does not associate to the access point

If the card accepts the essid, for example, by doing

iwconfig wlan0 essid YourESSID

but does not associate to the access point even when no encryption is needed: The driver seems to need the interface to be in the up state when it gets the essid. So first do

ip link set wlan0 up

then set the essid as before.

Identify wireless card

Running lspci -nn should list one of :

03:00.0 Network controller [0280]: Intel Corporation PRO/Wireless 3945ABG Network Connection [8086:4222] (rev 02)

03:00.0 Network controller [0280]: Intel Corporation PRO/Wireless 3945ABG Network Connection [8086:4227]

03:00.0 Network controller [0280]: Intel Corporation PRO/Wireless 4965 AG or AGN Network Connection [8086:4229]

03:00.0 Network controller [0280]: Intel Corporation PRO/Wireless 4965 AG or AGN Network Connection [8086:4230]

Using the latest kernel version of the driver

kernel 2.6.24 includes the iwlwifi driver in the kernel source, but it is quite an old version of the driver.

The website http://www.linuxwireless.org has the latest kernel driver sources, and instructions for using them with your existing kernel. In other words, you can update 2.6.24 with a much more recent driver version. Visit the download page, download the tar file, and follow the included readme. The 2.6.24 version of the driver is stable, but the latest versions have improvements in power management and suspend/resume behaviour.

iwlwifi