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

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

  • Update to version  first.
    300 series firmware link:
  • Use the relevant .ros file from inside the zip file. e.g. sx300_fw-13558.ros
  • Set as active image
  • reboot

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

  • Update the bootloader by loading in, for example, this file: sx300_boot-13506.rfb that is also in the zip file mentioned above.
  • Boringly, you can’t do this over http / https. You need to do it over TFTP. Which means you need to be onsite / connected over a stable VPN and have TFTP running on something.
  • Reboot

Fix part 3

Now with and updated bootloader – you can apply

  • Set as active image
  • reboot

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

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