I found WRTH54GS router's OS was not Linux but VxWorks. WRTH54GS is similar to WRTSL54GS in appearance. But it is different. (OS, USB port, perhaps ram) When I nmaped -A the router, the result was VxWorks and the router freezed. Whenever I nmaped the router, it always freezed. I don't know why. And in recent firmware I found that the source code was in MS windows. I opened the firmware with notepad.exe and searched with "vxworks". And I found this. D:/Project/VxWorks/WRTH54g/mips212/target/src/drv/mem/nvRamToFlash.c D:/Project/VxWorks/WRTH54g/mips212/target/src/drv/vme/nullVme.c gcc2_compiled. __gnu_compiled_c sysClkTicksPerSecond sysClkArg Is VxWorks compiled in MS Windows? Firmware http://www.linksys.ne.kr/linksysboard/board/up_file/pds/WRTH54GS.bin Model Pictures http://memolog.blog.naver.com/ferra888/4 http://www.iclub.co.kr/goods/network/wirelesslan/iclub_17846.html You can find the model in google search.