iPhone Dev Team has release Redsn0w 0.9.11b3 and 0.9.11b4 versions by updating their software. Some people got a “Restore failed” message when using this tool. They fixed this issue with b4 version. This b4 version tethered jailbreaking support with the 5.1.1 (you can use for A4 devices and earlier).

Download Redsn0w 0.9.11b4 for Windows

Download Redsn0w 0.9.11b4 for MAC