Router IOS files are normally stored in flash with the config file being stored in flash. In the event of a power outage or spike it is very common for these devices to become corrupt and so having a copy of the IOS and the startup configs for all devices backed up is a very good idea.
It could be that there is a new version of the IOS release and your device, whether it be a router or a switch may need to have an IOS upgrade
In general, a router should be backed up as soon as it has been configured. The IOS image can be stored in a secure location with other important files and data. These can be stored on a TFTP server and all the backups can be restored to the switch or router from this TFTP server
General IOS Upgrade
The IOS upgrade is carried out in privileged EXEC mode with the command:
Router#copy tftp flash
The administrator will then be prompted to enter the IP address of the TFTP server and then the router will request the filename of the IOS image.
If there is not sufficient flash memory storage available, the router will prompt the administrator to erase the contents of flash. Flash memory will be erased before the new image is downloaded.
It is important to maintain current versions of the IOS to eliminate security problems and performance problems. Newer releases are larger and may require flash and RAM upgrades.
Before the file transfer begins, it is good practice to ping the TFTP server from the router to ensure that there is a connection to the TFTP server
Common problems can occur when the file is supplied incorrectly, the IOS filenames do tend to be complex and the filename must be supplied accurately.
It may be a good idea to cut and paste the name of the file from a Windows Explorer directory listing or similar. The transfer should not take long, this is dependent on your connection speed, but the IOS is likely to be around 5 to 50Mb depending on the type of IOS.
Once the new IOS has downloaded, the router will restart. If the router fails to restart normally – follow the steps below.
Replacing a corrupt IOS
If you find that a router has stopped working and will not restart, or you have just attempted to upgrade an IOS and the process has not been successful, then you can install another IOS in two ways:
• Using xmodem to restore it via the console-this does not require a TFTP server and is much slower
• Using TFTP from ROM monitor mode(rommon). Faster Recommended
In order for the process to be carried out using xmodem, a copy of the IOS has to be stored on the PC the router is consoled in to. The command to achieve the xmodem transfer is:
As the IOS has not been successfully loaded you will have to use rom monitor mode (rommon) in order to carry out the steps. This is the built in cut down ios that is burned on to rom. The ROM monitor mode is identified by the prompt, which is rommon 1>
Using Xmodem to restore IOS
Rommon 1>xmodem –c image_file_name
Where the image file name is the files name and the –c argument is used for error checking.
Once the router is ready to accept the transfer you use your terminal emulator to send a file to the router via Xmodem. The file transfer will then start. Please note that the file transfer will be carried out at the speed of the console line which will probably be 9600. In order to speed up the transfer, you can increase the baud rate to the fastest the router can handle (usually 115200)
to do this in rommon
rommon 2 > confreg
load rom after netboot fails
console baud: 9600
boot: image specified by the boot system commands or default to: cisco-C2600
do you wish to change the configuration? y/n [n]: y
enable “diagnostic mode”? y/n [n]:
enable “use net in IP bcast address”? y/n [n]:
disable “load rom after netboot fails”? y/n [n]:
enable “use all zero broadcast”? y/n [n]:
enable “break/abort has effect”? y/n [n]:
enable “ignore system config info”? y/n [n]:
change console baud rate? y/n [n]: y
enter rate: 0 = 9600, 1 = 4800, 2 = 1200, 3 = 2400
4 = 19200, 5 = 38400, 6 = 57600, 7 = 115200 : 7
change the boot characteristics? y/n [n]:
load rom after netboot fails
console baud: 115200
boot: image specified by the boot system commands
or default to: cisco2-C3600
do you wish to change the configuration? y/n [n]:
You must reset or power cycle for new config to take effect. To do this type i (for initialise) and press return, the router will restart using a baud of 115200. Remember to set the baudrate of the router to 115200.
Once the transfer is complete, remember to set the baud back to 9600 and similarly change the baud on the terminal emulation software back to 9600 as well.
Using TFTP from Rommon to restore IOS
rommon 1> tftpdnld
The administrator will then need to input several variables of the type:
• The IP address of the LAN.
• The subnet mask.
• The default gateway.
• The IP address of the TFTP.
• The IOS filename on the server.
When the transfer is complete, restart the router using rommon 1>i If successful the router should reboot using the newly uploaded IOS
Upgrade IOS and obtain startup-config from TFTP
Ensure you have a copy of a suitable IOS and a working startup-config for your router. Store these on a TFTP server that is accessible from your network.
router#copy tftp flash
router#copy tftp running-config
Upgrade your IOS and download and install a running-configuration respectively. Remember to issue a copy run start command to save the running configuration to the routers NVRAM.
Once complete Issue a show version command to check the current IOS has been obtained from the TFTP server. Issue a show startup to confirm the startup-configuration has been obtained from the TFTP server.