[Cisco] - Use ROMmon to transfer an IOS in flash using TFTP

If you have deleted the IOS in memory from a Cisco router and rebooted the router, it will started in ROMmon (ROM Monitor) mode. 

Once you get ROMmon prompt, you will have to set some variable's values to be able to execute on IOS transfer from a TFTP server: ​

rommon 1 >IP_ADDRESS=10.0.0.1
rommon 2 >IP_SUBNET_MASK=255.0.0.0
rommon 3 >DEFAULT_GATEWAY=10.0.0.2
rommon 4 >TFTP_SERVER=10.0.0.2
rommon 5 >TFTP_FILE=c2800nm-advipservicesk9-mz.124-15.T1.bin
rommon 6 >tftpdnld

Once completed, use "reset" command to reboot the router. You can then make sure the IOS has been correctly transfered in flash memory using the following command: ​

Router#dir flash: