This is the third article on security awareness, still focusing on WiFi networks.

This article is about increasing the transmit power on a wireless network device within Linux.

For the purposes of having a good reception, and also for having the capability to transmit an adequate signal on a wireless network device, it is important to have the following:

• A wireless network device with high power capability, a good antenna and the ability for the device to be configured in Master mode (in this mode it will be capable of transmitting information). A good example is the Alfa AWUS036NH, which is a 2000 mW device, comes with a 5 dBi antenna (which can be replaced easily with a larger one, such as a 9 dBi antenna, if better reception is required) and it comes with a chipset that allows it to be configured in Master mode.
• A good location where other Access Points or clients can be sniffed (e.g. in between the client(s) and the Access Point), or where an Access Point will be useful to be set up for clients that will be accessing it.

Specifically, for setting up our own Access Point in a future article in this series, it can be useful to increase the transmit power of the device. By default this is usually set to 20 decibel (dB) or 22 dB. The transmit power is regulated and limited by local laws in countries. In many countries it is not allowed to transmit at higher levels. Some countries however do allow it, and it can be a simple matter of changing the country code for the device, to allow higher transmit power levels. For some more information on this topic, this is described in more detail here.

For example, for wireless device wlan2, you may see a transmit power of 20 dBm by running the "iwconfig" command:

# iwconfig wlan2
wlan2   IEEE 802.11  ESSID:off/any
        Mode:Managed  Access Point: Not-Associated  Tx-Power=20 dBm
        Retry short  long limit:2   RTS thr:off   Fragment thr:off
        Encryption key: off
        Power Management:off

For higher levels, you may try changing the country code to either Bolivia (BO) or Guyana (GY), where higher transmit levels are allowed. For example, to change it to 30 decibel:

# ifconfig wlan2 down
# iw reg set BO 
# iwconfig wlan2 txpower 30
# ifconfig wlan2 up

Or:

# ifconfig wlan2 down
# iw reg set GY
# iwconfig wlan2 txpower 30
# ifconfig wlan2 up

It may depend on the wireless device what transmit power is allowed, and what will work.

After changing the transmit power, confirm the current setting by running "iwconfig" again:

# iwconfig wlan2
wlan2   IEEE 802.11  ESSID:off/any
        Mode:Managed  Access Point: Not-Associated  Tx-Power=30 dBm
        Retry short  long limit:2   RTS thr:off   Fragment thr:off
        Encryption key: off
        Power Management:off

Please note here that changing the transmit power to higher levels than allowed in your country, may mean you are breaking a local law, and thus is not advised. The information provided here is only for educational purposes, and can provide you insight into what a hacker might use.



If you found this useful, here's more on the same topic(s) in our blog:

• Generate a random password
• Double X11 forwarding
• Resetting the Root Password of RHEL-7
• Secure shell access to HMC
• Changing a password without a prompt