Registartion values confuse

[zillah2004]

As we know,

1- To enter the ROM monitor mode, the configuration register value should be set to 0xnnn0.( format is ending with zero)

2-To boot from the first image in Flash or to boot to the IOS in ROM (platform dependant), set the configuration register to 0xnnn. (format is ending with one)

3- To configure the system to use the boot system commands in NVRAM, set the configuration register to any value from 0xnnn2 to 0xnnnF.( format is ending with one up to F)

Is this registration value differ from the one that tells the router to ignore (pay pass) the startup-configuration or do not pay pass, which are 0x2142 and 0x2102 respectively, and both of them have the format of 0xnnn2!!!which are similar to number 3

[Harold Ritter]

Here's a link to an excellent tool that helps understanding the config-register values and how they affect the router behavior:

Boson Confreg Calculator:

http://www.boson.com/promo/utilities.htm

Hope this helps,

[Kevin Dorrell]

I agree, I think there is a logical ambiguity here. Let us look at the standard password recovery value, 0x2142. Bit 6 (0x..4.) says "ignore nvram", but bit 2 (0x...2) say "load according to the "boot system" command in NVRAM. So which is it to be? If the config register is 0x2142 and NVRAM says "boot system rom", or a different image, then what does it do, take the first image, or the one specified in the NVRAM you told it to ignore?

I tried the Boson tool, and I am not too clear on the results from that either.

To get a proper handle on this, I think I am going to try it on a real router. I'll let you know.

Kevin Dorrell

Luxembourg

[zillah2004]

Kevin.Dorrell

I need to double check with you:

You said: "0x2142. Bit 6 (0x..4.) says "ignore nvram", but bit 2 (0x...2) say "load according to the "boot system" command in NVRAM"

You did you mean by bit 6 ? and bit 2? Could you please let me know, just to follow with you

[Kevin Dorrell]

Sorry, my turn to correct myself now. I meant bit 6 and bit 1 respectively. That is counting in binary from the least significant bit as bit 0. So:

Bit 0 - 0x...1

Bit 1 - 0x...2

Bit 2 - 0x...4

Bit 3 - 0x...8

Bit 4 - 0x..1.

Bit 5 - 0x..2.

Bit 6 - 0x..4.

Bit 7 - 0x..8.

Bit 8 - 0x.1..

Bit 9 - 0x.2..

etc

So bit 6 is the bit that makes the '4' in 0x2142.

Kevin Dorrell

Luxembourg

[zillah2004]

May be it will help :

"The configuration register is a 16-bit register in NVRAM that is represented as 4 hexadecimal digits.

The lowest four bits of the configuration register form the boot field"

Now our concearn about least significant hexadecimal value

0= ROM Monitior

1= ROM IOS

2-15=Startup-config in NVRAM

Depend on this criterion we should not concern about second hexadecimal value (our case is 4)

[zillah2004]

Just to correct some missing letter:

2- instead of 0xnn, it should be 0xnnn1 (add number 1 at end)

3- instead of (fromat is ending with one up to F), it should be:(fromat is ending with two up to F)