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CISCO Router configuration register

 
 
Willy the Wisp
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      04-28-2006
Hello,

i want to know what a router do if the configuration register is set to
0x2102.

In some lyrics i found that in this case it prevents the successfull loading
of the Cisco IOS from flash memory.

But also i found this explantion:

" The factory-default setting for the configuration register is 0x2102,
which indicates that the router should attempt to load a Cisco IOS image
from flash memory."

??

So I hope someone can help me with this problem.

Greets



 
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ttrotter01@yahoo.com
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      04-28-2006
The router will boot up from the start-up config that is in NVRAM, if
there is one and will tell it to boot from the first IOS on flash, or
the one specified in your start up config. This number can be changed
in order to make the router do different things. For example, 0x2101
if you do not want it to boot from the default IOS. 0x2142 will tell
the router not to boot up from the startup config, mostly used for
doing password breaks. Hope this helps.

 
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Doan
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      04-28-2006
On 28 Apr 2006, http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:

> The router will boot up from the start-up config that is in NVRAM, if
> there is one and will tell it to boot from the first IOS on flash, or
> the one specified in your start up config. This number can be changed
> in order to make the router do different things. For example, 0x2101
> if you do not want it to boot from the default IOS. 0x2142 will tell
> the router not to boot up from the startup config, mostly used for
> doing password breaks. Hope this helps.
>

The configuration register is a 16-bit register. Each bit has a specific
meaning:
15 - Diagnostic mode disabled
14 - Ip broadcast do not have network numbers
13 - Boot default ROM software if network boot fails
12-11 - Console speed is 9600 baud
10 - IP broadcasts with ones
8 - Break disabled
7 - OEM disabled
6 - Ignore configuration disabled
03-00 - Boot file is ...
Boots Field Parameters 0x0000
Stays at the system bootstrap prompt 0x0001
Boots system image on EPROM 0x0002-0x000F
Specifies a default netboot filename

http://www.cisco.com/en/US/products/...ig-reg-meaning

Doan

 
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Peter
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      04-28-2006
Hi Willy,

> i want to know what a router do if the configuration register is set to 0x2102.


Warning: Some Config Register bit values can vary between device
MODELS, so it does help to correctly identify the Model for a valid
reply. The "default" setting for Cisco Routers is usually 0x2102, but
for Cisco Etherswitches it is usually 0x102. Mixing Router default
settings with Switch defaults can cause great confusion........ I
once found such a problem were a layer 2/3 Switch should have used
0x102 but was actually set to 0x2102 and a wrong version IOS was
always loaded from FLASH (it always loaded the SECOND IOS in flash
regardless of Config statements to the contrary.). There are detailed
docs on the Cisco Web site for ALL products, I recommend that you read
them for definitive statements.

Assuming you have a Router with a setting of 0x2102, this will cause a
Router to boot "normally".
From power on, "normally" usually includes -
1. BOOTROM will load and perform simple functional tests, and then
check if the BREAK key has been pressed to halt a "normal" boot. If
Break HAS been pressed it NOTES THIS, but does not stop at that point!
2. BOOTROM will then read the startup-config to see if BREAK has
been disabled. If it has not been disabled and BREAK WAS pressed,
BOOTROM then exits to ROMON mode, otherwise it continues.
3. BOOTROM will then read the startup-config to see if a specific
VERSION(s) of IOS are defined to be loaded from either TFTP, FTP or
FLASH.
4. If there is 1 or more specific version loads requested, then
BOOTROM will try them IN ORDER, before falling back on the default of
loading the FIRST valid IOS image it finds in FLASH. If it can't find
a VALID FLASH image to load, it halts in ROMON (BOOTROM) mode.


> " The factory-default setting for the configuration register is 0x2102,
> which indicates that the router should attempt to load a Cisco IOS image
> from flash memory."


That is a very simple overview of the process as config statements can
enforce other options (EG TFTP load) before it tries to boot from
whatever it finds in FLASH.

I hope this helps..............................pk.


--
Peter from Auckland.
 
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theapplebee theapplebee is offline
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Join Date: Jun 2009
Location: USA
Posts: 67
 
      11-04-2009
See Cisco page to see details about register value

http://www.cisco.com/en/US/products/...8022493f.shtml

Sharing Cisco Expertise : www.ipBalance.com
 

Last edited by theapplebee; 04-17-2010 at 04:12 PM..
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