Cisco Switch – Use IOS Bootable USB Drive to Recover 3750x

Its possible that over time or when uploading new firmware to a switch the firmware that the switch is using to boot will become corrupt, in this case you will be left at a “switch:” prompt and will need to recover the IOS on the device. Below are the steps to do that assuming that you already have a known working USB drive formatted in FAT 16 which is able to Boot IOS images and is loaded with the one you need and that image is also validated as working.

One thing to note that if you had to manually get to the ‘switch:’ prompt because it was stuck in a boot loop make sure you boot up to the image version that was last working on the device because if it has to do a microcode update it will reboot at the end of that process and get stuck back into the boot loop and you will have to preform these steps twice to fully boot.

 

First you will need to make sure Flash is initialized:

Validate your image is on your flashdrive:

Boot to an image on the USB drive:

At this point just wait until the image is fully loaded and you can login, as long as your configuration file did not get corrupt it should be loaded with the same config.

Once logged in copy the image you need from the flash drive to the internal flash memory of the switch:

Run an MD5 checksum on the image on the USB drive and the image on the internal Flash storage and make sure they match:

At this point we know we have a good image sitting on the internal flash.

Lastly make sure that the boot variable is set to the name of your image that you just copied to the switch

if it is not you can set it properly with the command “boot system flash:/path/to/image.bin” with ‘/path/to/image.bin’ being the path to your image on your switch.

Now reboot the switch and it will use your image you copied and should boot up with no problems.

 

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