It is possible to boot a Cisco router off of a USB flash drive.  This can come in real handy if you are on-site and the compact flash of the router is bad.  Here are the steps to do it: [more]

  1. Format your USB flash drive with a FAT file system.  This needs to be FAT and not FAT32.
  2. Copy the system IOS image to the USB flash drive.
  3. While the router is powered off, plug in the USB flash drive to the USB port on the router.
  4. Power on the router and when it starts to boot up press the Break key to enter ROMMON mode.
  5. Once in ROMMON mode enter the following command to boot to USB:
    • boot usbflash0:<system image file name>    (e.g. boot usbflash0:1841-advsecurityk9-mz.124-23.bin)

The following link has some more information about what is supported: