Portal

https://chenliang0571.wordpress.com/2013/12/08/openwrt-wifidog-wifi-hotspots/
http://www.h3c.com.cn/MiniSite/Technology_Circle/Technology_Column/WLAN/WLAN_Technology/201210/756111_97665_0.htm
http://talk.withme.me/?p=222
http://wiki.openwrt.org/toh/start#raspberry_pi_foundation