Config registers

Can somebody let me know about config registers.
i guess the default is 0 x 2102 (show version).
How much more should i dwelve on these registers.

Please advise.

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techman-aka-Format

hey ragu, 2102 is the default for nvram. 101 is rom, and 2402 is password recovery, I believe. Hope this helps.

sanjana

The configuration register is a 16-bit register.0-15

So in that 0-3bits r called boot feild.

We will have 15 combination from these boot feild sequence:
So

If boot field is 0x0= the router will enter ROM monitor mode

0x1=The IOS image stored in ROM will be loaded

0x2 to 0xF = The router will boot as normal and load default Ios
image stored in Flash and enables boot system
commands.

That is the story of first 4 bits.

And 0x04 and 0x05 has no significant meaning.

And is each bit is set to 1 from 0x06, the register has significant meaning :

The significance is mentioned below:

Bit number that is set
0x06=causes system software to ignore NVRAM contents.This is also
used for password recovery.

0x07=OEM bit enable.

0x08= Break disable.

0x09 is unused bit.

0x10=IP broadcast with all 0's.

0x11-0x12=used for console line speed

with these two bits we will have 4 combinations:

bit 11 bit 12 Baud rate

0 0 9600

0 1 4800

1 0 1200

1 1 2400

0x13=Boot default Flash software if network bootfails.

0x14=IP broadcast do not have network number.

0x15=enable diagnostic messages and ignore NVRAM contents

Hence we set each and every bit in configation register it has their corresponding significance value as mentioned above.

Note:
Default configuration register value is 0x2102.

configuration register vaue for password recovery is 0x2142 i.e with sixth bit set to '1'.

configuration register vaue is set by using the command config-register value in global configuration mode.

To show the settings of configuration register vaue we have to use the command show version at privelege mode.

That's it u have to know about the configuration register settings.

All the best for ur exam.

Webmaster

The information about the config-register required for the CCNA exam can also be found in one of our TechNotes:

www.techexams.net/technotes/ccna/basic_router_management.shtml

ragu

thanks guys.

i really appreciate it

seth223uk

if the config register is 0-15 bits then why is password recovery 0x2142? what is the 0 and x for and why is there an 0/r in front of some of them?
can anyone clear up these nuances?

kulkarni_anupam

0X stands for Hexadecimal notaion. if u have 0X infront of any decimal number it means u have to view it as a hex number. If you want to convert a number into a hex number you translate the given number into binary then seperate that number into 4 bit regions and then calculate the decimal value of each nibble( 4 bit region).
so 0X2102 means the following
2 = 0010
1 = 0001
0 = 0000
2 = 0010
so 0X 2102 = 0010 0001 0000 0010
these are 16 bits. i.e 0 -15
now if u remember from the book, the 6th bit is used for password recovery. so u turn the 6th bit on.
so the binary number that u get is as follows
0010 0001 0100 0010
remember the 6th bit is actually in the 7th position from the right. this is because of the numbering convention. we always write 16 bits as 0 to 15 and not 1 to 16.
so comming back to the point. the above binary numbertranslates to 0X 2142. this is wht u shud remember for password recovery.
2402 is not password recovery as someone earlier mentioned.
this shud clear things. if u dont get it u better get down and do some background work

seth223uk

i get it mate thanks alot that has cleared up any nuances i didnt get thanku