Configuration Register on Cisco IOS

This topic is to discuss the following lesson:

Hi Rene,
what is the default value of Configuration register 2101 or 2102 ?? I am little bit confused that you have write here .Thx


Hello Mohammad

You are correct. 2102 is the default value for most Cisco platforms. I will let @ReneMolenaar know to fix the typo.

Thanks again!


It’s fixed, sorry for the confusion!

Dear ReneMolenaar can I get latest Pactracer and do have new book ccna 200-301 by you.

Hello Ahmed

You can go to Cisco’s Packet Tracer site, sign up to a free Cisco packet tracer course, and download the software for free.

As for Rene’s books, for the time being, he has all the CCNA 200-301 lessons at the following link:

He can will let you know if there will also be a book coming out for CCNA 200-301.

I hope this has been helpful!


Hello Ahmed,

At the moment I don’t have any plans to release new books. For now, I focus completely on


Dear Team of Network Lesson,
As the default configuration register value is 0x2102 but as I checked this on my real switch then it shows (0XF), instead of default value so why it doesn’t show the default value and what does mean (0XF) please see the output.

Ajmal Ahmady
Configuration Register

Hello Ajmal

The issue with the config register is that it can be various values, and still function correctly. This document describes in detail all of the possible values for the config register. Even though it says “routers” it is the same for switches as well:

Now the 0x2102 is default for routers, but other devices like switches may have other values. Specifically, the 0xF is a normal config value for switches like the 2960 and the 4500 series for example. According to the documentation above, any value between 0x0002 and 0x000F does the following:

Specifies a default netboot filename. Enables boot system commands that override the default netboot filename.

In other words, it will boot up using the default filename of the IOS bin file, but allows you to interrupt this process to override it if you choose to. This is normal behaviour.

I hope this has been helpful!


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Thank you Sir,



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Where exactly the Config Register values stored??

is it in ROM ??

Hello Narad

The configuration register is actually stored in the NVRAM itself. Not in the configuration file, of course, but still within the NVRAM memory.

I hope this has been helpful!