Don’t panic. You haven’t downloaded the wrong file. You’ve just encountered Cisco’s .
Unlike a standard AireOS firmware update (which changes the operating system features), an FUS updates the —specifically the bootloader and the PowerPC boot code . air-ct2500-k9-2-0-0-0-fus.aes
Here is exactly what this file is, why you need it, and how to use it without bricking your controller. FUS stands for Field Upgrade Software . Don’t panic