"My notes about Configuration Register on Cisco Routers" on Show IP Protocols

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"My notes about Configuration Register on Cisco Routers" on Show IP Protocols

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My notes about Configuration Register on Cisco Routers Posted: 03 Mar 2014 07:23 PM PST This page on Cisco.com defines all details about "Configuration Register" on Cisco routers. http://www.cisco.com/c/en/us/support/docs/routers/10000-series-routers/50421-config-register-use.html The Purpose of the Configuration Register The configuration register can be used to change router behavior in several ways, such as: how the router boots (into ROMmon, NetBoot) options while booting (ignore configuration, disable boot messages) console speed (baud rate for a terminal emulation session) Configuration registers are indeed DIP switches on most of PC motherboard. DIP-Switch as part of a PCB from 1976, by Rainglasz. Captured on Wikipedia. So the following table captured on above post should be renamed to "Position of DIP switch". The positions are numbered from 0 to 15. Totally there are 16 DIP switches. Position of DIP switch Bit Number Hex Meaning 00-03 0x0000-0x000F Boots Field Parameters: 0x0000 - Stays at the system bootstrap prompt. 0x0001 - Boots the first system image in onboard Flash memory (EPROM). 0x0002-0x000F- Specifies a default netboot filename. Enables boot system commands that override the default netboot filename. 06 0x0040 Ignore NVRAM contents 07 0x0080 Disable boot messages 08 0x0100 Break disabled 10 0x0400 IP broadcast with all zeros 5,11,12 0x0020, 0x0800, 0x1000 Console line speed 13 0x2000 Boots default ROM software if network boot fails 14 0x4000 IP broadcasts do not have net numbers 15 0x8000 Enables diagnostic messages Ignores NVRAM contents Two most frequently used combinations are: All routers' factory default: "0x2102" Ignores NVRAM, or when we forget password to login and we want to do a password reset: "0x2142". Configuration Register Setting Router Behavior 0x102 Ignores break 9600 console baud 0x1202 1200 baud rate 0x2101 Boots into bootstrap Ignores break Boots into ROM if initial boot fails 9600 console baud rate 0x2102 (Factory Defauly) Ignores break Boots into ROM if initial boot fails 9600 console baud rate default value for most platforms 0x2120 Boots into ROMmon 19200 console speed 0x2122 Ignores break Boots into ROM if initial boot fails 19200 console baud rate 0x2124 NetBoot Ignores break Boots into ROM if initial boot fails 19200 console speed 0x2142 (Ignores NVRAM, also for password reset) Ignores break Boots into ROM if initial boot fails 9600 console baud rate Ignores the contents of Non-Volatile RAM (NVRAM) (ignores configuration) 0x2902 Ignores break Boots into ROM if initial boot fails 4800 console baud rate 0x2922 Ignores break Boots into ROM if initial boot fails 38400 console baud rate 0x3122 Ignores break Boots into ROM if initial boot fails 57600 console baud rate 0x3902 Ignores break Boots into ROM if initial boot fails 2400 console baud rate 0x3922 Ignores break Boots into ROM if initial boot fails 115200 console baud rate Cheers!

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