The router can load an IOS image from the following locations:
- Flash
- TFTP server
- ROM (limited version of the IOS software)
Use the boot system command in global configuration mode to identify alternate locations for the IOS image. Use the copy command to archive, upgrade, or replace an IOS image.
| Use . . . | To . . . |
| Router(config)#boot system flash | Identify an IOS image file in flash to use at boot. |
| Router(config)#boot system tftp | Identify an IOS image file on a TFTP server to use at boot. |
| Router(config)#boot system rom (IOS versions 11.2 and below) Router(config)#boot system flash bootflash: (IOS versions 12.0 and above) | Specify to use the limited IOS version stored in ROM at boot. |
| Router#copy tftp flash | Restore the IOS image from backup on the TFTP server to Flash. |
Note: When you use the boot system command, you are not making backup copies of the IOS image, nor are you replacing the default IOS search order. You are directing the router where to look for the IOS image on boot-up. It tries each location in turn, until it finds a valid IOS image. If one is not found, it returns to the default load sequence.
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