need explanation of register bits

[denodave]

trying to find a CLEAR explanation of the codes and uses of the register bits for 1600/1700/2500/2600 series IOS 11.x or 12.x >> you know, what does the first bit do and what does a two mean as opposed to a four, and so forth.

I am hoping one of you kind folks has it on their fingertips, I am working on CCNA and having trouble deciphering some of their documentation! Email me! denodave@yahoo.com
Real men pray...especially techies!

 

[CCIEWANNABE]

The answer depends on the value the configuration register, which can be changed to set various system parameters. Certain bits are assigned to specific functions. Recall, the configuration register contains 16 bits that read, left to right, 15-0. For the test, and during your career, bear this fact in mind: The default configuration register setting on Cisco routers is 0x2102.Fine, you say, what the heck does that mean. First of all, the 'x' in 0x2102 is not a multiplication symbol or even a letter. It is a number, read as part of this larger number. It means that bits 13, 8 and 1 are 'on' (recall, a computer knows only two things: on and off. On = 1. Off = 0). It all looks like this:

Configuration Register 2 1 0 2
Bit number 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Binary..... 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0

So you see the 2102 part of the number. You get the rest by adding the prefix 0x to the configuration register address. The 0x means the digits that follow are in hexadecimal.

Bit Hex What it does
00-03 0x000-0x000F Boot field (see below)
05 0x0020 Enables recurrence of the CONFIG_FILE.
06 0x0040 Ignore NVRAM contents
07 0x0080 Enables OEM bit
08 0x0100 Disable break function (good for password recovery)
09 0x0200 Uses secondary bootstrap
10 0x0400 Broadcast an IP with all zeros
11-12 0x0800-0x1000 Set console line speed (default is 9600 bps)
13 0x2000 If the network boot fails, boots from flash memory.
14 0x4000 Excludes network numbers from IP broadcasts.
15 0x8000 Enable diagnostic message and ignore NVM contents.
All copied and pasted from an article written by a crammsession author.

I'm not going to go into depth about the configuration register but I do want to talk about the four lower-order bits. These comprise the boot field and, depending on its value, the router will try to load the IOS software image system from ROM or from a user defined location. You can see the value of the configuration register by using the 'show version' command.So, if the boot field defines the source of the IOS software image required to boot and run the router, then we need to look at it carefully in terms of the router boot sequence. This is a breakdown of the boot field and what each setting means:
Boot Field 00 Meaning the ROM Monitor Mode. The configuration register is set to 2100. When the power is turned on, the system will remains at the ROM monitor prompt (rommon>). The user must enter a command to manually boot the router.


Boson's configuration register
LINK:
calculator

http://download.boson.com/downloads/utils/bos_calc.exe

All cramsession lost link sorry.
Route once; switch many

 

[cpace]

I am using a great program called config-register decoder.
Not sure where I got, but it tells what settings match confreg numbers.

 

[denodave]

Thank you! You folks just cleared it all up for me. I was having a bit of brain clogging where the hex format was concerned. I wasn't clear on the fact that each decimal digit in the register code represents a four-bit part of the sixteen-bit code in hex (gotta remember xxxx.xxxx.xxxx.xxxx). Email me! denodave@yahoo.com
Real men pray...especially techies!