Why configuration register

What is the Purpose of 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 Set and display the configuration register value Force the router into the ROM monitor bootstrap program Select a boot source and default boot filename Enable or disable the Break function Control broadcast addresses Load operating software from ROM To view the setting of the Configuration Register, use the following Router show version Cisco Internetwork Operating System Software IOS tm Software CJS-L , Version Processor board ID , with hardware revision Bridging software.

TN Emulation software. Enables boot system commands that override the default netboot filename. Proudly powered by WordPress Theme nuwhite by Mkhuda. If the boot field is set to 3 binary on a Cisco , the default boot name is cisco If several boot system commands are in the configuration, they are attempted in the order that they appear. Example shows the configuration for a router where it first attempts to boot an image from flash, and if that fails, to boot from a TFTP server, and if that fails, to boot from ROM.

This section covers a sample boot sequence for a MC router. For the test, you must have a high level of familiarity with the boot sequence of a router. Following are the four stages:. The first stage of the boot sequence is the loading of bootstrap software. The bootstrap software initializes the CPU and launches the bootloader:.

System Bootstrap, Version The second stage of the boot sequence is the bootloader. The bootloader is not a full router image. It contains minimal functionality for reading the configuration and accessing the flash file system highlighted. The router at this point can act as an end host with no routing functionality. If the bootloader is not present, the router attempts to load the first file present in the flash file system. Related posts: No related posts.

Ethernet Collisions and Troubleshooting. Leave a Reply Cancel reply Your email address will not be published. Contact info ipcisco. Subscribe to NewsLetter. IPCisco is the Winner! The following boot field values determine if the router loads an operating system and where it obtains the system image: When the entire boot field equals 0x0 , the router does not load a system image.

Instead, it enters ROM monitor or "maintenance" mode, from which you can enter ROM monitor commands to manually load a system image. When the entire boot field equals 0x1 , the router loads the boot helper or rxboot image.

When the entire boot field equals a value between 0x2 and 0xF , the router loads the system image specified by boot system commands in the startup configuration file. When the startup configuration file does not contain boot system commands, the router first tries to load a valid image from the default Flash device, and then if one does not exist it tries to load a default system image stored on a network server.

When loading a default system image from a network server, the router uses the configuration register settings to determine the default system image filename for booting from a network server. The router forms the default boot filename by starting with the word cisco and then appending the octal equivalent of the boot field number in the configuration register, followed by a hyphen - and the processor type name cisconn-cpu. See the appropriate hardware installation guide for details on the configuration register and the default filename.

The following flow chart shows, in more detail, how the configuration register value and initial state of the router dictate the manner in which the Cisco device will boot. For more information on rebooting a Cisco router, see Rebooting a Router Note: document is in.