Cisco Small Business Switches – Firmware update issue / failure / not working

3rd August 2022

Cisco Small Business Switches. SF300, SG300 etc


Particularly the older ones, fail to update to the latest firmware (currently


Complains of “illegal” file format or something similar.



Can’t go from very old firmware to latest version in one step.

And that is very poorly documented  / hard to find on the site.


Fix part 1

If you try and then go to now, it might work, depending on the exact model of switch, but you might also get a failure that complains about the file being “too large” / “too big”.

Fix part 2

Fix part 3

Now with and updated bootloader – you can apply

then all that’s left to do is apologise to users who have had 3 switch reboots in quick succession.