Managing IOS images using Xmodem

Managing IOS images using Xmodem

5.2.5

This page will explain how ROMmon and Xmodem can be used to restore IOS software images. If the IOS image in flash has been erased or corrupted, the IOS may need to be restored from the ROM monitor mode (ROMmon). In many of the Cisco hardware architectures, the ROMmon mode is identified by the rommon 1> prompt. This first step in this process is to identify why the IOS image did not load from flash. This could be due to a corrupt or missing image. The flash should be examined with the dir flash: command. If an image is located that appears to be valid, the user should attempt to boot from that image. This is done with the boot flash: command. For example if the image name is c2600-is-mz.121-5, the command is as follows: rommon 1>boot flash:c2600-is-mz.121-5 If the router boots properly, the user should check two items to determine why the router did not use the IOS image from flash and booted to the ROMmon instead. First, use the show version command to check the configuration register to ensure that it is configured for the default boot sequence. If the configuration register value is correct, use the show startup-config command to see if there is a boot system command that instructs the router to use the IOS for ROMmon. If the router will not properly boot from the image or there is no IOS image, a new IOS will need to be downloaded. To recover the IOS file, a user can use Xmodem to restore the image through the console or use TFTP to download the image from the ROMmon mode.

Download with Xmodem from ROMmon

To restore the IOS through the console, the local PC needs to have a copy of the IOS file to restore and a terminal emulation program such as HyperTerminal. The IOS can be restored with the default console speed of 9600 bps. The baud rate can be changed to 115200 bps to speed up the download. Use the confreg command to change the console speed from ROMmon mode. After the confreg command is entered, the router will prompt for the parameters that can be changed. When the “change console baud rate? y/n [n]:” prompt appears, if the user selects y, the router will prompt the user to select the new speed. After the console speed is changed, restart the router into ROMmon mode. The terminal session at 9600 bps is terminated and a new session is started at 115200 bps to match the console speed. The xmodem command can be used from the ROMmon mode to restore an IOS software image from the PC. The format of the command is xmodem -c image_file_name. For example, to restore an IOS image file named c2600-is-mz.122-10a.bin, use the following command: xmodem -c c2600-is-mz.122-10a.bin   The -c instructs the Xmodem process to use cyclic redundancy check (CRC) for error checking during the download. The router will prompt the user to not begin the transfer and present a warning message. The warning message will inform the user that the bootflash will be erased and will ask for confirmation to continue. When the process is continued, the router will then prompt to start the transfer. Now the Xmodem transfer needs to be started from the terminal emulator. In HyperTerminal, select Transfer > Send File. In the Send File popup specify the image name and location, select Xmodem as the protocol, and start the transfer. The Sending File popup will display the status of the transfer. After the transfer is complete, a message will indicate that flash is being erased. This is followed by the “Download Complete!” message. Before the router is restarted, set the console speed back to 9600 and the config register back to 0x2102. Enter the command config-register 0x2102 at the privileged EXEC prompt. While the router reboots, end the 115200 bps terminal session and begin a 9600 bps session. The Lab Activities will teach students how to gain access to a router to recover a password and how to manage IOS images with ROMmon and Xmodem. The next page will introduce the ROMmon environment variables.