How to upgrade Cisco IOS for a Cisco router?

This is a very basic but important knowledge when you supporting cisco router. It can prevent unpredictable software bugs and even some security vulnerabilities. Below showing the simple steps on how to upgrade cisco IOS using a PC, which directly connected to a cisco router:-

1.) Establish connectivity between PC and router
Use a cross cable to connect PC and the router. Configure IP address to PC and router. For example, use the private IP address, such as 10.0.0.0/30. Do a ping test to verify both connectivity. Make sure the PC's firewall does not block port 69, because this port is used by tftp server as listening port.

2.) Setup tftp server
I use 3CDaemon as my TFTP server, which is freeware. You can find it and download it at here. Install and configure default directory for the tftp server.

3.) Get the IOS file ready
Copy the cisco IOS file, that you want upgrade to the router, into the tftp default directory. Make sure the router specification is fulfill the memory and space requirements of this IOS file. Use "show version" command at router to double check on the router memory and flash.

4.) Get the router ready
Console to router, type "format flash:" command to delete all files in flash. Use "delete flash:[existing IOS file name]" command if want to delete a single file. Use "Copy flash tftp" to backup the existing IOS file into the PC.

5.) Start IOS upgrade
Type "copy tftp flash". Router will prompt you to enter tftp server IP address then follow by the IOS file name. Enter the your PC's IP address and the IOS file including the file extension (.bin). You will see it running exclamation mark until it finish.

6.) Reload router
Router must be reloaded to run the new IOS. Use "show version" to verify.

For more details and example, you can browse to http://www.bdsltd.co.uk/network/cisco/upgrade.htm

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