Configuration Register Mistake

Unanswered Question
Oct 16th, 2008

I have a Cisco Routers LAP

one of my trained students puts by mistake on a router Configuration Register 0x1242

I can not now loggin in Router by console ( unfortunately no other ports configured to access )

what can we do to take it back ?

Regards,

I have this problem too.
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Joe Clarke Thu, 10/16/2008 - 06:29

It depends on the router type. For modern routers, connect to the console, then power-cycle the router. Right after the initial ROM version banner, send a break sequence to the router. If using Hyperterm, this is a Control+Break (all possible break sequences are listed at http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a0080174a34.shtml). This should give you a rommon prompt. From here, you can type:

confreg 0x2102

Then type boot to continue to boot the device. Different routers require different steps. You should search Cisco.com for the password recovery procedure for your router. When it says to set the config-register to 0x2142, set it to 0x2102 instead.

srihari4cisco Thu, 12/03/2009 - 07:23

Hi,

I have a similar issue with 1721 router. and it worked at 57600 BAUD rate.The best solution is to check with all BAUD rates.

and please note these points.

15 14 13 12 | 11 10 9 8 | 7 6 5 4 | 3 2 1 0

4  3    2   1    4   3  2 1 4  3 2 1   4 3 2 1

now you come to know that what are the confreg values you have entered.

After that find what was the change you made with the help of it.

Bit Number

Hex

Meaning

00-03

0x0000-0x000F

  • Boots Field Parameters 0x0000

  • Stays at the system bootstrap prompt 0x0001

  • Boots system image on EPROM 0x0002-0x000F

  • Specifies a default netboot filename

06

0x0040

  • Ignore NVRAM contents

07

0x0080

  • Disable boot messages

08

0x0100

  • Break disabled

10

0x0400

  • IP broadcast with all zeros

5,11,12

0x0020, 0x0800, 0x1000

  • Console line speed

13

0x2000

  • Boots default ROM software if network boot fails

14

0x4000

  • IP broadcasts do not have net numbers

15

0x8000

  • Enables diagnostic messages

  • Ignores NVRAM contents

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