DD-WRT is free Linux-based firmware for several wireless routers, most notably the Linksys WRT54G (including the WRT54GL and WRT54GS) and Buffalo WHR-G54s,WHR-HP-G54. It is licensed under the GNU General Public License version 2. Many of DD-WRT's features are not included in typical router firmware. These features include support for the Kai network, daemon-based services, IPv6, Wireless Distribution System, RADIUS, advanced quality of service, radio output power control, overclocking capability, and software support for a Secure Digital Card hardware modification. Since DD-WRT v24 there is support for some PowerPC, IXP425-based router boards, Atheros WiSOC and X86 based systems.