Cisco Systems CCNA 2 5.2.7 Environment variables , 5.2.8 File system verification

The default console speed of 9600 bps can be used or it can be changed to 115200 bps. This

will speed up the download. The console speed can be changed with the confreg command.

To restore the IOS image from the PC, students should use the xmodem command. The

format of the command is xmodem –c image_file_name. The -c instructs the Xmodem

process to use CRC to check for errors during the download. The router then sends a warning

message that the bootflash will be erased. Now the Xmodem transfer needs to be started from

the terminal emulator. Instruct students to select Transfer > Send and then specify the image

name and location in the Send File popup. Select the xmodem protocol and start the transfer.

After the download is complete, the console speed must be changed back to 9600 bps and the

configuration register should be changed back to 0x2102. This is done with the confreg

0x2102 command.

5.2.7 Environment variables

The IOS can also be restored from a TFTP session. The fastest way to restore an IOS image

from the router is to use TFTP from ROMmon to download the image. This is done with the

tftpdnld command. The environmental variables provide a minimal configuration. To set a

ROMmon environment variable, the name is typed, followed by an equal sign (=) and the value

for the variable. All variable names are case sensitive. The minimum variables required to use

the tftpdnld command are as follows:

• The IP address of the LAN

• The subnet mask

• The default gateway

• The IP address of the TFTP

• The IOS filename on the server

Discuss these procedures with the students and make sure they understand each concept.

Also stress the fact that the fastest way to restore an IOS image to the router is to use TFTP

from ROMmon to download the image.

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5.2.8 File system verification

There are several commands used to verify the router file system. One is the show version

command. This command is used to check the current image and available flash. It also

verifies the source of the IOS image and the configuration register boot field setting. The show

flash command is also used to verify the flash system. This command identifies the amount

of flash that is available. It also confirms that there is ample space to store a new IOS image.

Configuration files may contain boot system commands. These identify the source of the

desired boot IOS image. Multiple boot system commands are used to create a fallback

sequence to discover and load an IOS. Boot system commands are processed in the order of

their appearance in the configuration file.