Configuration Register Mistake

ahmedsalahomar · ‎10-16-2008

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,

Joe Clarke · ‎10-16-2008

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.

ahmedsalahomar · ‎10-28-2008

Thanks,

It works at bit rate 1200

srihari4cisco · ‎12-03-2009

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