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Losing the IOS

I have alot of cisco 3550 switches out at different sites. So far we have been rebooting all switches and when they power back up the IOS is missing.

I end up using xmodem to get them working.

What could cause the IOS to be lost.



May you please post the show run command output as well.



Also post the output of

dir flash:c3550-i5k2l2q3-mz.121-22.EA4

dir zflash:c3550-i5k2l2q3-mz.121-22.EA4

And the show run


I can give the sh run what are you looking for note this switch booted up fine after reboot it is some of the switches that loose the IOS

switch10#dir flash:c3550-i5k2l2q3-mz.121-22.EA4
Directory of flash:/c3550-i5k2l2q3-mz.121-22.EA4/

    7  drwx        4032  Feb 28 1993 19:04:43 -05:00  html
  441  -rwx     4968676  Feb 28 1993 19:06:57 -05:00  c3550-i5k2l2q3-mz.121-22.EA4.bin
  442  -rwx         263  Feb 28 1993 19:06:57 -05:00  info

15998976 bytes total (9503744 bytes free)
switch10#dir zflash:c3550-i5k2l2q3-mz.121-22.EA4
Directory of zflash:/c3550-i5k2l2q3-mz.121-22.EA4/

    7  drwx        4032  Feb 28 1993 19:04:43 -05:00  html
  441  -rwx     4968676  Feb 28 1993 19:06:57 -05:00  c3550-i5k2l2q3-mz.121-22.EA4.bin
  442  -rwx         263  Feb 28 1993 19:06:57 -05:00  info

15998976 bytes total (9503744 bytes free)

We would need to see this for the switches that lost the IOS.


I would also like to see it to because I am not sure what is causing this seems 1 out 10 cisco 3550 fail to boot up after reload and it just started to happen.

I will start to gather that info for sites going forward and see if I find anything. Wasn't sure if someone had same problem and new a reason why old equipment etc.

This could be a bug. Are you running all the same level of IOS for all the swithes? Also could you upgrade the IOS on one of the switches and reboot it to see if the IOS remains.

I have had switches lose the config on reboot but not the IOS itself. Mine ended up being a bug in the IOS which had to do with a kron job trying to run to a location that was no longer valid.

actually could you run the following command on a few of the problem switches and post the output......  show file descriptors


File Descriptors:

  No open file descriptors

and it is the same IOS on all switch 2,000 switches

Version 12.1(22)EA4

I am at a loss on what would cause this. I would open a TAC case if you can to see if there is a bug that would be causing this, or you could check you IOS in the bug tracker tool.


Leo Laohoo
VIP Community Legend

Configuration register is 0x10F

Shouldn't this be 0xF?


When you say after reload the switch looses ios, this means after the reload the switch goes to rommon mode correct ?

if it goes to rommon then do a "dir flash:" this will show you if there is any IOS image in the flash or not.

If there is no IOS image there then its possibly due to currupted flash

However if the ISO image is there issue a "boot" command in rommon the switch will come up with the IOS in flash.

Then its an issue with the boot variable or configuration register. Check the output of "show boot"

the boot variable field should have the IOS and config register should be 0x2102.

If you open a TAC case let me know i can take owenership of it and help you out. My id vvasisth

Hope that helps and if this does then dont forget to rate the post.


Varun Vasisth

A register value of 0x10f indicates that the switch config-register is set to the default.  Indicating that the switch was either never configured properly to start with or that it has reverted to the default.

This also is the reason your having a problem.  The IOS could be valid and intact and this will not mean jack because 0x10f will boot the BOOT environmental variable.  However, by default this is blank.  Since you are able to load the IOS manually this indicates to me that the IOS is most likely valid and without error.  Another indication that the IOS is not the primary issue is that if the IOS was bad or that the flash was bad it would boot into ROMMON as the cisco employee already posted.

Your symptoms do not indicate a bad IOS or bad flash as they have been described and as I read them.

You can change the config-register and you do so by running the enabled command "set boot config-register (value)" i.e. "set boot config-register 0X2102"

I would set the config-register and then reload.  If the switch reverts and goes back to 0x10f then I would look at faulty hardware as my next step.

If this doesn't fix your problem but the switch is retaining 0x2102 as the config-register then let us know and we can do additional troubleshooting for that issue.


before someone comments and contradicts 0x10f is the default.  I should clarify and say that it is the default value for the CATOS.  Cisco IOS doesn't have this value, to my knowledge, and hence why it is a little harder to know.  Afterall, who uses CATOS anymore?


Also if you get an error when you do "set boot config-register" (which is the valid CATOS command) then try  the config command "config-register (value)".  That is the valid IOS command to change the config-register value. 

the config reg has never been changed I also get the switches with that. I can't even figure how to change it on a 3550

I have switches coming in daily with this problem so I will be open a tac case shortly

This isn't a TAC issue.

You have switches coming in that were previously configured to use CatOS.  Then you throw on a IOS and your not configuring them properly to use a valid config-register value for IOS.  Hence why you have the problem you do.

These are cisco WS-C3550-24 NO CATOS

and is 0x10F is default for cisco 3550 switch and I am not sure if that can be changed

WS-C3550-24 is the model.  CatOS and Cisco IOS both work on 3550 and if you are getting these devices used then it is very possible the previous owner used CatOS on them.  If they were sold to you new then I would question that they were actually new devices and not refurbs or something is wrong because I don't think resellers can sell the WS-C3550-24 with CatOS pre-installed anymore.

When you take in a new switch the 1st couple of steps should include identifying the config-register and then if it is a CatOS value you change it to a Cisco IOS value.  tftp the correct Cisco IOS over and then reload the switch so that it boots up properly into Cisco IOS.  Make a final verification of the Switch config-register and version of IOS running.

I suspect that since you didn't know how to do this that these steps were being skipped during intake.

Just so your clear here are the 3 most common scenarios and commands to set/change the config-register.

ROMMON: confreg [value]

CatOS: (enabled) set boot config-register [value]

Cisco IOS: (config) config-register [value]



rommon 1 >confreg 0x2102


Console> (enable) set boot config-register 0x10f

Cisco IOS:

Switch(config)#config-register 0x2102

I just went to check and test this recommendation and it didn't validate the config-register command.  Then I remembered that the 3550 doesn't come with the command config-register.  I have two 3550 48's next to me so I will try and replicate your issue and see what I come up with.

In the meantime I would follow this guide:

See if the steps provided there allow you to set the boot more effectively.  For all of your other switches the register value is most likely settable.  The reason the 0x10f is the default for the 3550's you have is because the 3550's were designed and built, initially, for CatOS.