Missing or corrupted image on Cisco Sx500 switch.


In this article we will see how we can fix the problem if Cisco 500 or 300 series SMB switches don’t boot because of either corrupted or missing firmware image. I will be using Cisco SF500-48P but the procedure should be the same for all Cisco 500 and 300 series switches.

Problem description

Your 500 or 300 series Cisco switch constantly reboots and you see a similar output when connected to console port:

The error says that check sum control for firmware image fails. We will need to upload another firmware file which has .ros extension. At the top we can see the following BOOT Software Version Built 23-Nov-2011 08:31:59. This is the version of boot code file which boots first and then loads the actual firmware.

Important! The version of the firmware file should match the version of boot code file, otherwise the switch may not work properly.


Step 1. Terminal emulator

Before we start make sure you are using a terminal software which supports XMODEM protocol, because it will be used for uploading a new image file. I am using Tera Term which is free and pretty popular.

Step 2. Download the firmware file

Go to Cisco Download website and download a new image file which has .ros extension. Make sure its version matches the version of your boot code file as much as possible. For example, my boot code version is and the closest version match for firmware file on the Cisco website is

Make sure the file you download has .ros extension:

Step 3. Interrupt the boot process

Press ESC or Enter during the boot and you will see the following menu:

Choose Download Software and the switch will start trying to get a new firmware file using XMODEM protocol.

Now, go to File->Transfer->XMODEM->Send of Tera Term and select the firmware file you downloaded from Cisco website:

Once you select the file, the emulator will begin transferring the file which can take quite a long time (~20 minutes) because of low console speed:

Once the file transfer is finished the switch will reboot and you will get the familiar Username: prompt.

Step 4. Check for error message

Make sure that you don’t get any incompatibility errors during boot process like this:

If you see an error like this it means that your firmware file is not compatible with the boot code file. In the example shown above the boot code file version was but firmware version was which caused this error.


Once you get a web access to your switch you can update both boot code and firmware files. Thank you for reading:)

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