0x102 or 0x2102

[emiliano.eusebio]

Hi,

Can someone explain me which is the difference in configure the conf-reg value in 0x102 or 0x2102?

Thanks a Lot

Emiliano

[Peter Paluch · Accepted solution]

Emiliano,

See the following document for a great explanation:

http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a008022493f.shtml#config-reg-meaning

Best regards,

Peter

[dapurwin]

@Peter Paluch The document may offer some good insight, but what it does not address is the OP's original query. 

What is the difference between the (2) values?  My research and experience with a 93k switch that refuses to boot into 2102, but stubbornly remains at 0x102 (even after stating that after reboot, the new value will become 0x2102) is that the two values are identical.  

0x102=0x2102  Can anyone prove this wrong?

[Peter Paluch]

Hello @dapurwin,

I believe that the document actually answers the original poster's question well :) What is different is your particular platform.

On many switches, including Catalyst 9300, the configuration register is not used and has no meaning. It is there only for backward compatibility with the stub IOS code, and perhaps with user scripts that look for the value in the outputs. Whatever value you save there, it will be ignored, and on the next boot, it will be replaced with the hardcoded value (in fact, I doubt that the value is even stored anywhere in hardware - it is quite possible it is fully emulated). Catalysts 2950, 2960, 3560, 3750, for example, used to have the configuration register value fixed at 0xF. Catalyst 9300 has the value fixed at 0x102 - but, once again, no component on the switch actually uses this value during boot.

For all intents and purposes, the configuration value on Catalyst 9300 is a meaningless hardcoded value.

Best regards,
Peter

[Dave-LC]

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@dapurwin wrote:

@Peter Paluch The document may offer some good insight, but what it does not address is the OP's original query. 

What is the difference between the (2) values?  My research and experience with a 93k switch that refuses to boot into 2102, but stubbornly remains at 0x102 (even after stating that after reboot, the new value will become 0x2102) is that the two values are identical.  

0x102=0x2102  Can anyone prove this wrong?

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I used the Confreg tool to check it out. The difference is very small.  2102 includes fallback to booting from ROM if netboot fails. 0x102 does not fallback to ROM. Please see screenshots.