很多年前，经高人指点，
在笔记本上装Debian的wifi一直用下面的方法：
先在/etc/apt/sources.list 添加 non-free
然后用下面两句命令
apt update
apt install firmware-iwlwifi
一直非常顺利，直到最近用Debian 9 安装两台T410/T420遇到了同样的问题，用原来的方法安装firmware-iwlwifi但发现不了无线网，在网上找了不少帖子，但还是不得要领，所以需要专家指点。
下面是目前的状况：
uname -a
Linux ThinkPad 4.9.0-11-amd64 #1 SMP Debian 4.9.189-3+deb9u1 (2019-09-20) x86_64 GNU/Linux
lspci -knn | grep -iA2 net
00:19.0 Ethernet controller [0200]: Intel Corporation 82577LM Gigabit Network Connection [8086:10ea] (rev 06)
Subsystem: Lenovo 82577LM Gigabit Network Connection [17aa:2153]
Kernel driver in use: e1000e
Kernel modules: e1000e
--
03:00.0 Network controller [0280]: Intel Corporation Centrino Advanced-N 6200 [8086:4239] (rev 35)
Subsystem: Intel Corporation Centrino Advanced-N 6200 2x2 AGN [8086:1311]
Kernel driver in use: iwlwifi
lshw -C net
*-network
description: Ethernet interface
product: 82577LM Gigabit Network Connection
vendor: Intel Corporation
physical id: 19
bus info: pci@0000:00:19.0
logical name: enp0s25
version: 06
serial: 00:26:2d:fe:64:8d
size: 100Mbit/s
capacity: 1Gbit/s
width: 32 bits
clock: 33MHz
capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=3.2.6-k duplex=full firmware=0.12-1 ip=192.168.1.108 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
resources: irq:24 memory:f2600000-f261ffff memory:f2625000-f2625fff ioport:1820(size=32)
*-network
description: Wireless interface
product: Centrino Advanced-N 6200
vendor: Intel Corporation
physical id: 0
bus info: pci@0000:03:00.0
logical name: wlp3s0
version: 35
serial: be:71:c0:02:27:55
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
configuration: broadcast=yes driver=iwlwifi driverversion=4.9.0-11-amd64 firmware=9.221.4.1 build 25532 latency=0 link=no multicast=yes wireless=IEEE 802.11
resources: irq:28 memory:f2400000-f2401fff
dmesg|grep iwl
[ 10.747495] iwlwifi 0000:03:00.0: can't disable ASPM; OS doesn't have ASPM control
[ 10.795505] iwlwifi 0000:03:00.0: firmware: direct-loading firmware iwlwifi-6000-4.ucode
[ 10.795652] iwlwifi 0000:03:00.0: loaded firmware version 9.221.4.1 build 25532 op_mode iwldvm
[ 10.851389] iwlwifi 0000:03:00.0: CONFIG_IWLWIFI_DEBUG disabled
[ 10.851390] iwlwifi 0000:03:00.0: CONFIG_IWLWIFI_DEBUGFS disabled
[ 10.851391] iwlwifi 0000:03:00.0: CONFIG_IWLWIFI_DEVICE_TRACING disabled
[ 10.851393] iwlwifi 0000:03:00.0: Detected Intel(R) Centrino(R) Advanced-N 6200 AGN, REV=0x74
[ 10.852583] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 10.940410] ieee80211 phy0: Selected rate control algorithm 'iwl-agn-rs'
[ 13.750028] iwlwifi 0000:03:00.0 wlp3s0: renamed from wlan0
[ 23.111234] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.118141] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.118233] iwlwifi 0000:03:00.0: Radio type=0x1-0x3-0x1
[ 23.342117] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.349036] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.349127] iwlwifi 0000:03:00.0: Radio type=0x1-0x3-0x1
[ 23.446053] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.452963] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.453055] iwlwifi 0000:03:00.0: Radio type=0x1-0x3-0x1
[ 23.678544] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.685461] iwlwifi 0000:03:00.0: L1 Enabled - LTR Disabled
[ 23.685553] iwlwifi 0000:03:00.0: Radio type=0x1-0x3-0x1
lshw -numeric -class network
*-network
description: Ethernet interface
product: 82577LM Gigabit Network Connection [8086:10EA]
vendor: Intel Corporation [8086]
physical id: 19
bus info: pci@0000:00:19.0
logical name: enp0s25
version: 06
serial: 00:26:2d:fe:64:8d
size: 100Mbit/s
capacity: 1Gbit/s
width: 32 bits
clock: 33MHz
capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=3.2.6-k duplex=full firmware=0.12-1 ip=192.168.1.108 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
resources: irq:24 memory:f2600000-f261ffff memory:f2625000-f2625fff ioport:1820(size=32)
*-network
description: Wireless interface
product: Centrino Advanced-N 6200 [8086:4239]
vendor: Intel Corporation [8086]
physical id: 0
bus info: pci@0000:03:00.0
logical name: wlp3s0
version: 35
serial: ca:56:d9:d1:6c:73
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
configuration: broadcast=yes driver=iwlwifi driverversion=4.9.0-11-amd64 firmware=9.221.4.1 build 25532 latency=0 link=no multicast=yes wireless=IEEE 802.11
resources: irq:27 memory:f2400000-f2401fff
nmcli dev status
DEVICE TYPE STATE CONNECTION
wlp3s0 wifi disconnected --
enp0s25 ethernet unmanaged --
lo loopback unmanaged --
iwconfig
lo no wireless extensions.
enp0s25 no wireless extensions.
wlp3s0 IEEE 802.11 ESSID:off/any
Mode:Managed Access Point: Not-Associated Tx-Power=15 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
iw dev wlp3s0 info
Interface wlp3s0
ifindex 3
wdev 0x1
addr ce:5a:75:cc:2e:f3
type managed
wiphy 0
txpower 15.00 dBm
