Linux Wireless Configuration Module – cfg80211

If you travel frequently and have to access wireless internet in that country, you’d be better to check this article. Sometimes, in foreign country, you would face with unaccessible wireless AP.

One of the possible reason is that you use the different country code which is described in IEEE 802.11 regulatory domain code? from the code in that country use. Depends on this country code, it will choose proper frequency ranges

In Linux box, you can change this by cfg80211 module. Following is the information of cfg80211 module.

[root@dhcp-160-193 ~]# modinfo cfg80211
filename: /lib/modules/2.6.18-194.el5/kernel/net/wireless/cfg80211.ko
description: wireless configuration support
license: GPL
author: Johannes Berg
srcversion: 5575C55ADCFBE1371A2CF5E
depends: rfkill,wireless_compat
vermagic: 2.6.18-194.el5 SMP mod_unload gcc-4.1
parm: ieee80211_regdom:IEEE 802.11 regulatory domain code (charp)
module_sig: 883f3504ba0377778ccfeaa942826a…

You can find more information about cfg80211 in here: http://wireless.kernel.org/en/developers/Documentation/cfg80211#About_cfg80211?

If you are in Korea, you can change the region code by modify /etc/modprobe.conf

options cfg80211 ieee80211_regdom=KR

You can see the details of changing frequency in /var/log/messages such as following:

 

cfg80211: Calling CRDA to update world regulatory domain
cfg80211: World regulatory domain updated:
        (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp)
        (2402000 KHz - 2472000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
        (2457000 KHz - 2482000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
        (2474000 KHz - 2494000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
        (5170000 KHz - 5250000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
        (5735000 KHz - 5835000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
cfg80211: Calling CRDA for country: KR
cfg80211: Regulatory domain changed to country: KR
        (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp)
        (2402000 KHz - 2482000 KHz @ 20000 KHz), (N/A, 2000 mBm)
        (5170000 KHz - 5250000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
        (5250000 KHz - 5330000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
        (5490000 KHz - 5630000 KHz @ 20000 KHz), (300 mBi, 3000 mBm)
        (5735000 KHz - 5815000 KHz @ 20000 KHz), (300 mBi, 3000 mBm)
It will make you can access the AP’s in the country you stay.

 

Comment: Just realized that it works for EU and JP. Also, NIC needs to be have capability for that frequencies which you are want to use.

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