Environment variables

Environment variables

5.2.7

This page will explain what the ROMmon environment variables are and how they are used.
The IOS can also be restored from a TFTP session. The fastest way to restore an IOS image to the router is to use TFTP from ROMmon to download the image. To do this, set the environmental variables and then use the tftpdnld command.
Since the ROMmon has very limited functions, no configuration file is loaded during boot. As a result, the router has no IP or interface configuration. The environmental variables provide a minimal configuration to allow for the TFTP of the IOS. The ROMmon TFTP transfer works only on the first LAN port so a simple set of IP parameters are set for this interface. To set a ROMmon environment variable, type the variable name, then the equal sign (=), and the value for the variable. For example, to set the IP address to 10.0.0.1, type IP_ADDRESS=10.0.0.1 at the ROMmon prompt. 

Note: All variable names are case sensitive.

The minimum variables required to use tftpdnld are as follows:

• IP_ADDRESS - The IP address on the LAN interface
• IP_SUBNET_MASK - The subnet mask for the LAN interface
• DEFAULT_GATEWAY - The default gateway for the LAN interface
• TFTP_SERVER - The IP address of the TFTP server
• TFTP_FILE - The IOS filename on the server

Use the set command to check the ROMmon environment variables. 
Once the variables are set for the IOS download, the tftpdnld command is entered with no arguments. The ROMmon will echo the variables and then a confirmation prompt will appear with a warning that this will erase the flash. 
As each datagram of the IOS file is received, an exclamation point (!) will be displayed. When the complete IOS file has been received, the flash will be erased and the new IOS image file written. Appropriate messages will be displayed as the process is completed.
When the new image is written into flash and the ROMmon prompt is displayed, the router can be restarted by entering the reset command or typing i. The router should now boot from the new IOS image in flash.
The next page will describe some commands that can be used to verify a router file system.

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.

Managing IOS images using TFTP

Managing IOS images using TFTP

5.2.5

The page will show students how to store IOS images on a TFTP server.
The IOS may need to be backed up, upgraded, or restored using the copy command. When a router first arrives, the IOS should be backed up. The IOS backup can be initiated from the privileged EXEC mode with the copy flash tftp command. This IOS image can be stored in a central server with other IOS images. These images can be used to restore or upgrade the IOS on the routers and switches in a network. This server should have a TFTP service running. The router will prompt the user to enter the IP address of the TFTP server and to specify a destination filename.
To restore or upgrade the IOS from the server use the copy tftp flash command as shown in Figure . The router will prompt the user to enter the IP address of the TFTP server. Next, the router will prompt the user for the filename of the IOS image on the server. The router may then prompt the user to erase flash. This often happens if there is not sufficient flash available for the new image. As the image is erased from flash, a series of e’s will appear to show the erase process.
As each datagram of the IOS image file is downloaded, an exclamation mark (!) will be displayed. This IOS image is several megabytes and may take a long time to download.
The new flash image will be verified after it is downloaded. The router is now ready to be reloaded to use the new IOS image.
The Lab Activity will allow students to back up a copy of a router IOS onto a TFTP server.
The next page will show students how ROMmon and Xmodem can be used to manage IOS images.