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New Member

Rommon...

Hi there!

I'm a little confused and hope that someone knowledgeable will be kind enough to help me out.

I don't quite understand the difference between 0x2100 and 0x2142 (re the configuration register).

Am I right in thinking that booting the router with 0x2100 will not ignore NVRAM whereas booting the router with 0x2142 will ignore NVRAM?

My next question is why would I want to boot the router with 0x2100? I ask because I know 0x2142 is used for password recovery.

Thank you in advance for your help.

Peace and blessings to all,

Kind regards,

Ashraf.

6 REPLIES
Silver

Re: Rommon...

Hi Ashraf,

There are different values for config register to persform various things. but i don't find anything on 0x2100 and also where u found this as a config register value.

As u said, 0x2142 will ignore the nvram and will be used during password recovery.

If u want to know the various values and their use, just go thro.

http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a008022493f.shtml

Rate if it does,

Rgs,

New Member

Re: Rommon...

Hi there! Thank you very much for your reply.

Unfortunately, I'm still a little confused as I've found a number of references to the configuration register having a value of 0x2100. The first reference is in Todd Lammle's CCNA Study Guide, 5th Edition on page 435. Another of the many references is on link:

http://www.cisco.com/public/scc/compass/common/activities/Tool-confreg.htm

Both mention the Boot Field of 00 being ROM Monitor mode.

So, my question is, if 0x2100 is ROMMON then, why have another value of 0x2142?

New Member

Re: Rommon...

Hi there!

Having thought long and hard about it, I think the reason for preferring 0x2142 over 0x2100 is so that you don't lose your current IOS image.

By entering 0x2100, you are actually by-passing the loading of any IOS images. Therefore, to not lose the IOS image, one enters 0x2142, loads the IOS image from Flash (or gets it from TFTP) and enters Setup Mode for password recovery, which then loads the config file into RAM.

Or, at least, that's what I think is happening. I'd very much appreciate it if someone can confirm this.

Thank you all in advance for your help.

Kind regards,

Ashraf.

Hall of Fame Super Silver

Re: Rommon...

Ashraf

I would be more comfortable if your answer did not talk about losing the image with config register of 0x2100 and perhaps talked about ignoring the image or bypassing the image. With 0x2100 the image is not gone, and it is not lost, it is just not loaded. This is almost exactly the same idea as 0x2142 does not lose the config but simply ignores the startup config.

I believe that for the purpose of this discussion we should focus on the last digit of the config register and ignore the first three. If the last digit is 0 then it instructs the router to boot directly into rommon. If the last digit is 1 it instructs the router to boot into rxboot mode. If the last digit is any value from 2 to f it instructs the router to boot the normal image.

In the same way that there are sometimes troubleshooting situations where you might want to ignore the statup config (0x2142) there may be some circumstances where you want to control the image as the router boots (0x2100 or 0x2101, or even perhaps 0x2140). One aspect of this is that on run from flash routers like the 2500 series the flash was read-only while the router was running its normal image. You would want rxboot mode or rommon to get the flash read-write so that you could put a new image there.

HTH

Rick

New Member

Re: Rommon...

Dear Rick,

Hi there! Thank you very much for your help!!! It certainly has cleared up my misunderstanding.

Thank you again. I wish you peace, love and happiness.

Kind regards,

Ashraf.

New Member

It talks about the

It talks about the configuration register 0x2100 on page 831 of ICND 1 100-105.

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