Boot Cisco router from USB in ROMMON

When helping a colleague at work who was struggling to get the correct IOS image onto a ISR4431 I came across this tip that I never knew, in later versions of ROMMON you can boot from USB.

All you need to do is:

1) Ensure router is powered off
2) Insert USB stick with IOS image on
3) Boot router into ROMMON
4) Type the command: boot usbflash0:

Obviously the “usbflash0” may change dependant on platform and which slot you plugged the stick into.

This is really helpful if the IOS is corrupted or missing.

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