Firmware Auto Fall Back Mechanism - Cisco ISA500 Series Administration Manual

Device Management
Firmware Management
Cisco ISA500 Series Integrated Security Appliance Administrator Guide
After you switch to the secondary firmware, the security appliance automatically
reboots with the saved settings.

Firmware Auto Fall Back Mechanism

The security appliance includes two firmware images in the same NAND flash to
provide an Auto Fall Back mechanism so that the security appliance can
automatically switch to the secondary firmware when the primary firmware
occurs a CRC (Cyclic Redundancy Check) Error or cannot boot up successfully for
five times.
The Auto Fall Back mechanism operates as follows:
1. When the security appliance tries to boot up with the primary firmware, the
Bootloader checks the CRC of the primary firmware.
2. If the primary firmware occurs a CRC Error or a Boot Failure, the Bootloader will
switch to the secondary firmware and check the CRC for the secondary
firmware.
• CRC Error: An error that the firmware cannot pass the CRC validation.
Downloading an incomplete firmware or incompletely writing the firmware
to the flash may cause the CRC error.
• Boot Failure: A failure that the firmware cannot boot up successfully for five
times. Booting up successfully means that the system boots to the login
shell.
3. If the secondary firmware occurs a CRC Error or a Boot Failure, the Rescue
mode starts up. In the Rescue mode, the security appliance works as a TFTP
server. You can use a TFTP client to upload a firmware image to upgrade. The IP
address of the TFTP server is 192.168.1.1. For more information about the
Rescue mode, see
page 302.
Using the Rescue Mode to Recover the System,
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