Recovering IOS Image

IOS Image is crucial for a router to run. However if the IOS Image is accidentally deleted from the flash, the router can still operate as long as it's not rebooted, because it's running IOS from RAM. If somehow it's rebooted or you have to reboot it for some reason, then the router won't be able to run IOS anymore, it will boot into ROMmon. You can recover from this state by copying IOS Image that has been backup previously to an TFTP server. But the steps/commands are different because we are dealing with ROMmon (you still can type "?" to see available commands in ROMmon). the steps are:

• step 1. Connect the router directly to the TFTP server. first you have to connect the router to the TFTP server from the first ethernet port of the router (this depends on the router, some router is FastEthernet0/0). And give the TFTP server a static IP address, for example 192.168.20.1.
  
• step 2. Set ROMmon variables. turn on the router then you'll see ROMmon prompt. some notes about variables in ROMmon:
  

Variable names are case sensitive


Don't include any spaces before and after the = symbol


Navigational key are not operatable

enter the following variables to the ROMmon, the value for each variable is just an example, you can change it like you need.

IP_ADDRESS=192.168.20.2
IP_SUBNET_MASK=255.255.255.0
DEFAULT_GATEWAY=192.168.20.1
TFTP_SERVER=192.168.20.1
TFTP_FILE=c1841-ipbase-mz.123-14.T7.bin

• step 3. enter the "tftpdnld" command. this will download the specified file from the TFTP server. before the transfer begin you'll be warned that all existing data in flash will be deleted. type "y" to continue. then you will see some exclamation marks "!", one exclamation mark shows you that a UDP packet has been successfully transferred. after it finished, use the "reset" command to reboot the router with the IOS Image in the flash.
  

Recovering Using Xmodem
there's also another way for recovering a IOS Image to a router. another way is using xmodem (ROMmon supports Xmodem), but the transfer progress is slower than using the "tftpddnld" command because the transfer is accomplished using the console cable. that is, copy of the IOS Image is not taken from a TFTP server but might be from an Administrator PC. the steps are:

• step 1. connect a PC that has the IOS Image to the router. Open connection with the router to enter the ROMmon command prompt.
  
• step 2. use the "xmodem" command at the ROMmon command prompt. the syntax is
  

xmodem [-cyr] [filename]

c : specifies CRC-16
y : specifies the Ymodem protocol
r : copies the image to RAM

example,

xmodem -c c1841-ipbase-mx.123-14.T7.bin

by entering this command at the router, will make the router ready to receive the specified file.

• step 3. from the software that you use to make a connection to the router through the console cable, choose to send a file. Depends on the software that you use, there should be a menu to send a file. if you use HyperTerminal the menu is Transfer > Send File.
  
• step 4. browse for the file that you want to transfer, specify the protocol to be used to xmodem, then send the file. after the transfer has been done the router will reload automatically with the new IOS Image.