[Gentoo][Wifi driver] Intel® Centrino® Advanced-N 6235

1. Download driver
   Linux* Support for Intel® Wi-Fi Adapters
   
2. Decompress the package
   tar xvf iwlwifi-6000g2b-ucode-18.168.6.1.tgz
   cd iwlwifi-6000g2b-ucode-18.168.6.1
   
3. Installation of the firmware is simply:
   # cp iwlwifi-6000g2b-6.ucode /lib/firmware
   

Reference:

• Linux* Support for Intel® Wi-Fi Adapters