Corrupted IOS

Unanswered Question
Aug 28th, 2008

How is it possible to detect the IOS is courrupted? What kind of problems will be facig if the IOS is corrupted? Will the router gets into only the rommon mode if the IOS is corrupted.

I have this problem too.
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satish_zanjurne Thu, 08/28/2008 - 21:14


1.For lower end devices( 2600,3800) yes!! switch or router will go to ROMMON mode most of the time..

2.For few High end device like Cisco 7304 router goes to boot mode router(boot)..that means here you have minimum boot image is not the complete you can download the actual IOS using "copy tftp disk" command and boot normally


Manjunatha Jayaram Fri, 08/29/2008 - 01:09


Thanks for the reply, but what will be the issue if the router is loading but all the interfaces are hanging and the led status of all ports are showing green even if there is no cable connected. when checking the running configuration it is not showing any of the interface configurations or interfaces. Will this problem will be solved when the IOS is upgraded.

satish_zanjurne Fri, 08/29/2008 - 01:51

If this is modular router try resettting the NM/WIC , if it is not working, try putting different module.

If the current IOS of router does not support the NM/WIC , then router will not detect the NM/WIC.

If module is detected & it is behaving suddenly this way , mostly module must have gone bad.

can you attach show tech of this router ??

Joseph W. Doherty Fri, 08/29/2008 - 03:12

How is it possible to detect the IOS is courrupted?

On some platforms and IOS images, you can use the verify command.

"What kind of problems will be facig if the IOS is corrupted? Will the router gets into only the rommon mode if the IOS is corrupted."

If the system, during attempted load, detects the image is corrupt, it shouldn't load it. If there's another valid image, depending on boot var settings and default boot device contents, it might load another image. Otherwise, it would normally drop into rommon.

If the system does actually load a corrupted image, results, for our purpose, are unpredictable. Could be similar to having faulty RAM with a non-corrupt flash IOS image.

Manjunatha Jayaram Mon, 09/01/2008 - 22:17

If I had connected the console and opened the hyperterminal as default settings and powered on the switch or router, what will be the output? Will the post section will be displayed in the terminal window even if the device speed settings was not set to default. Should the speed settings must be set correctly for getting the post section in termial window when the device is restarted.

Joseph W. Doherty Tue, 09/02/2008 - 03:02

Your RS232 client com settings, e.g. hyperterminal, will need to match the router's com settings. The default speed is usually 9600 on Cisco routers. I believe hyperterminal's default is slower, usually 2400. I would also set hyperterminal's flow control to none.

Manjunatha Jayaram Tue, 09/02/2008 - 19:37

I just want to confirm that when we configure the console speed of the router to a non default value and that configuration is saved to running/startup configuration. So if we restart the router will the router uses the default console speed of device till the IOS and Startup configuration is loaded or will it use the speed that we had set.

Joseph W. Doherty Wed, 09/03/2008 - 03:13

Not 100% positive. I believe if you change the console speed in ROMMOM, it resets to default with next reboot, but since you mention saving console speed in a saved running config, I would expect it to use that on next restart. This also assumes the config is not corrupt during startup.

If you're locked out of the box, you might be able to break in to it using the password recovery method.

Manjunatha Jayaram Wed, 09/03/2008 - 20:14

Is the password recovery method can be done only using hyperterminal application? if then for password recovery also should the console speed and the application speed must be matching. And when restarting the device will the console speed will be the default value till the IOS and Startup cofiguration is loaded even if the speed was changed in running configuration and saved?

Joseph W. Doherty Thu, 09/04/2008 - 03:48

Yes, password recovery can be done using hyperterminal. You need to use control-break (if I recall correctly) very early in the power-on boot sequence. This starts the router in ROMMOM and precludes the normal IOS from loading. (Documentation on the procedure can be found on the Cisco web site.)

Again, I'm not sure whether the console will start up at the usual default 9600 rate until the IOS loads.


You can also try connecting to the console, change RS232 settings, press enter, and see if a readable prompt appears. If it's only a speed difference, there aren't too many to try. If other RS232 parameters, beyond just speed, might have been changed, the setting options to try does become annoyingly large.

Manjunatha Jayaram Fri, 09/05/2008 - 03:03

Thanks for providing these information. I just want to confirm that the console will start at the default rate , so as to confirm the switch is not booting as it is not showing any changes when restarted. Thankyou for your reply .


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