If the former is not true and you need to get into the ROMmon prompt, then you will need to change the configuration register (typically 0x2102 as given by show version ) to 0x0 as follows.The first four bits of the configuration register comprise the boot field.The value of the boot field defines the source of a default Cisco IOS software image that will be used to run the router.If the value of the boot field is 0 (configuration register value of XXX0), on startup the system enters and remains in the ROM monitor mode (rommon), awaiting a user command to boot the system manually.
For more information on the software configuration register bit meanings, see Configuring the Software Configuration Register. To verify the configured value of the configuration register, use the confreg command as shown below. To make the router boot automatically from a default Cisco IOS software image, change the configuration register value as shown below. However, if the router still enters the ROMmon mode, it is probably because the device is unable to locate a valid Cisco IOS software image. The first thing you need to do then is to look for a valid Cisco IOS software image. To do this, issue the dir command for each available device, and look for a valid Cisco IOS software image. For example, to look for the IOS in the Flash, use the command shown below. The output above indicates that a valid image is indeed present in the Flash. However, there are times when a valid image does not exist on any of the devices or the image on the Flash might be corrupted. In these cases, a valid image has to be downloaded using Trivial File Transfer Protocol (TFTP) or by using the Xmodem procedure. Both these procedures can be carried out from the ROMmon mode. If this happens, in addition to getting a valid Cisco IOS software image, you might need to reseat the Flash or replace it, if it is damaged. These two modes are used for recovery andor diagnostic procedures. Cisco Hyperterminal Software Upgrade Procedure InstallationIf you do not see the usual router prompt, you should follow the recommendations below to proceed with the upgrade procedure installation. Copy a valid image on the Flash by following the procedures provided in this. This example Windows HyperTerminal is configured for 8-N-1 at 9600 bps. Cisco Hyperterminal Software Serial Port ToConnect your PCs serial port to the console port of the router. Typically, if the routers Cisco IOS software image and bootflash image are both corrupt, the router only comes up in ROMmon mode.
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