Please refer below links:

http://www.cisco.com/en/US/products/hw/routers/ps259/products_tech_note09186a008015bfac.shtml

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/31sga/configuration/guide/rommon.html

or refer this process:

On the console of the nonworking router while in ROMmon mode, use the set command to display the current settings, which the program will use to download the IOS via TFTP. (For a Cisco example of these steps, check out this Cisco documentation.)

For example, here are the settings you must set for the tftpdnld command to work:

rommon> set

IP_ADDRESS=10.253.100.126

IP_SUBNET_MASK=255.255.0.0

TFTP_SERVER=10.253.15.72

DEFAULT_GATEWAY=10.253.1.1

TFTP_FILE={the name of the IOS that is saved on the PC}

However, your settings may not contain any of the required variables for the tftpdnld command. By default, it may look something like this:

rommon 9 > set

PS1=rommon ! >

BSI=0

RET_2_RUTC=0

RET_2_RTS=

?=1

If this is the case, set the required variables. While it might seem obvious to use the set command to set the variables, you can actually set the variables simply by entering the name of the variable, the equal sign [=], and the value.

For example, to set the IP address of the broken router, you would use the following:

IP_ADDRESS=10.253.100.126

Final steps

After setting your values, run the tftpdnld command, which will replace the IOS. Listing A provides an example of how I restored a router.

An alternate approach to the tftpdnld command

However, if the tftpdnld command doesn't work for some reason, you can use the xmodem command to send the IOS over the serial console line. (For instructions for this process, check out this Cisco documentation.) However, if you decide to take this route, it's a good idea to change the baud rate on the console and your PC to 115,200 so it doesn't take more than four hours for an 8-MB IOS file to transfer over the 9600-baud console.

hope that helps.

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