Mon /etc/conf.d/net :
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dns_domain_lo="linux-system"
nis_domain_lo="linux-system"

modules=( "ifconfig" "!iwconfig" )

modules_eth1=( "wpa_supplicant" "!iwconfig" )
wpa_supplicant_eth1="-Dwext"
wpa_timeout_eth1=60

config_eth0=( "192.168.0.4/24"
               "fec0::4/64 ")
#routes_eth0=( " default via 192.168.0.4" )

config_eth1=( "192.168.0.3/24"
               "fec0::3/64 ")
#routes_eth1=( " default via 192.168.0.4" )

preup() {
        if test ${IFACE} = "eth1" ; then
                /etc/init.d/ipw3945d start
                modprobe ipw3945
                sleep 5
        elif test ${IFACE} = "eth0"; then
                modprobe r1000
                sleep 5
        fi
}

#postup(){
#       if test ${IFACE} = "eth1" ; then
#               wpa_supplicant -Dwext -i${IFACE} -c/etc/wpa_supplicant.conf -B
#       fi
#}

postdown() {
        if test ${IFACE} = "eth1" ; then
                modprobe -r ipw3945
                /etc/init.d/ipw3945d stop
        fi
}

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Mon dmesg :

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ieee80211_crypt: registered algorithm 'NULL'
ieee80211: 802.11 data/management/control stack, 1.1.13
ieee80211: Copyright (C) 2004-2005 Intel Corporation <jketreno@linux.intel.com>
ipw3945: Intel(R) PRO/Wireless 3945 Network Connection driver for Linux, 1.1.0mpr
ipw3945: Copyright(c) 2003-2006 Intel Corporation
ACPI: PCI Interrupt 0000:05:00.0[A] -> GSI 18 (level, low) -> IRQ 18
PCI: Setting latency timer of device 0000:05:00.0 to 64
ipw3945: Detected Intel PRO/Wireless 3945ABG Network Connection
ipw3945: Detected geography ABG (13 802.11bg channels, 23 802.11a channels)
ADDRCONF(NETDEV_UP): eth1: link is not ready
ADDRCONF(NETDEV_CHANGE): eth1: link becomes ready
ieee80211_crypt: registered algorithm 'TKIP'
eth1: no IPv6 routers present
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