If The Configuration Register Is Set To 0x2102, Where Will The System Look For Boot Instructions?
Configuration Register
What is Configuration Register?
Configuration Register is a special sixteen bits value that tin can be configured in Cisco routers. It is mainly used in three cases;
- To determine how the router boots
- To make up one's mind boot options
- To prepare console speed
During the boot, router checks its software and the configuration files. To determine these files, router firstly check Configuration Register. According to its value, router determines what to exercise.
Configuration Annals Configuration is peculiarly used for Router Password Recovery. And so, what are the values of this special number?
Configuration Annals 0x2102
The default value of Config Register is 0x2102. With Configuration Annals 0x2102 value, the router boots from NVRAM and the normal router precedures works. The configuration stored in NVRAM is the startup configuration. And so, if nosotros need to featherbed this configuration, nosotros can change the default value. Especially during Router Password Recovery, this simple configuration is done.
We can check this value on Cisco routers with "show version" command. At the output of "prove version" command, Configuration Register value will be at the bottom.
Router# bear witness version
Cisco IOS Software, C800 Software (C800-UNIVERSALK9-M), Version 15.2(4)M4, RELEASE SOFTWARE (fc2)
Technical Support: http://world wide web.cisco.com/techsupport
Copyright (c) 1986-2013 by Cisco Systems, Inc.
Compiled Thu xx-Jun-13 xvi:14 by mnguyen
ROM: System Bootstrap, Version 15.2(2r)T, RELEASE SOFTWARE (fc1)
Router uptime is 35 minutes, 14 seconds
Organisation returned to ROM by power-on
System image file is "flash:c800-universalk9-mz.SPA.152-4.M4.bin"
…
Configuration register is 0x2102
Config Register 0x2142
To bypass NVRAM configuration, in other words, to bypass start-up configurataion, we tin can modify Config Register value. Here, the new value that we volition ready will be Configuration Annals 0x2142.
How to Change Configuration Register?
In that location are ii way to alter Config Register on a router. This can be done both in Rommon mode and in configuration style.
In Rommon manner, it can exist change with "confreg" command. Beneath, nosotros are irresolute Configuration Register as 0x2142.
rommon > confreg 0x2142
After this configurationi nosotros should reset the router to use this new value,or to force the router boot through this config register.
The other mode is configuring on configuration mode with "config- register" control.
Router# configure final
Router(config)# config-annals 0x2142
After configuration, you can cheque the ne value and exist sure about the value.
Router# show version
Cisco IOS Software, C800 Software (C800-UNIVERSALK9-M), Version xv.2(4)M4, RELEASE SOFTWARE (fc2)
Technical Back up: http://www.cisco.com/techsupport
Copyright (c) 1986-2013 by Cisco Systems, Inc.
Compiled Thu twenty-Jun-xiii 16:14 by mnguyen
ROM: System Bootstrap, Version 15.2(2r)T, RELEASE SOFTWARE (fc1)
Router uptime is 35 minutes, 14 seconds
System returned to ROM by power-on
System paradigm file is "wink:c800-universalk9-mz.SPA.152-4.M4.bin"
Configuration annals is 0x2102 (will be 0x2142 at next reload)
Again, we should reload the router for the new config annals to take effect.
Router# reload
System configuration has been modified. Save? [yes/no]: northward
Keep with reload? [confirm]
You can observe the detailed information about Config Register on Cisco Page.
If The Configuration Register Is Set To 0x2102, Where Will The System Look For Boot Instructions?,
Source: https://ipcisco.com/lesson/configuration-register/
Posted by: sussmanciary1980.blogspot.com
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