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Configuration Registers
The global configuration command - config-register is used to modify the behavior of the router. Weather or not it boots from saved configuration. Weather or not it boots from the flash or the boot-proms.The boot field is bits 0-3 (4 bits) in the configuration register
0xABCD
- The value range is from 0x0 to 0xFFFF
- 0x2102 is the factory-default configuration register value.
- 0x2142 boots from flash without using NVRAM contents good for password recovery.
- 0x2101 boots from boot prom image not flash, good for upgrading image on flash.
- 0x2141 boots from boot prom and ignores NVRAM contents.
- The third digit from the left (C) enables or disables Break. If the third digit is not 1, Break is enabled.
- 0x141, which disables the Break key, ignores the NVRAM configuration, and boots the default system image from ROM. Notice that 0x141 and 0x0141 are the same. We drop leading zeros in Hexadecimal.
- To enable the router to read the nonvolatile RAM configuration, clear the ignore NVRAM contents bit (0x0040).
| Monitor Command | Function |
| o | Displays the virtual configuration register, currently in effect, with a description of the bits |
| o/r | Resets the virtual configuration register to the defaults as follows: 9600 baud console UART speed break/abort has no effect ignore the system configuration NVRAM boot from ROM |
| o/r 0xvalue | Sets the virtual configuration register to the (hex) value, value Enter the i command after entering the o/r command to automatically reboot the router. |
| Bit No.(1) | Hexadecimal | Meaning |
| 00 to 03 | 0x0000 to 0x000F | Boot field |
| 06 | 0x0040 | Causes system software to ignore NVRAM contents |
| 07 | 0x0080 | OEM bit enabled |
| 08 | 0x0100 | Break disabled |
| 10 | 0x0400X | IP broadcast with all zeros |
| 11 to 12 | 0x0800 to 0x1000 | Console line speed |
| 13 | 0x2000 | Boot default ROM software if network boot fails |
| 14 | 0x4000 | IP broadcasts do not have net numbers |
| 15 | 0x8000 | Enable diagnostic messages and ignore NVRAM contents |
This value is a combination of the following:
bit 13 = 0x2000
bit 8 = 0x0100
bits 00 through 03 = 0x0002.
Explanation of Boot Field (Configuration Register Bits 00 to 03)
| Boot Field | Meaning |
| 0x0X | Stays at the system bootstrap prompt |
| 0x1 | Boots system image in system ROM |
| 0x2 to 0xF | Specifies a default netboot filename Enables boot system commands that override default netboot filename |
| Baud | Bit 12 | Bit 11 |
| 9600 | 0 | 0 |
| 4800 | 0 | 1 |
| 1200 | 1 | 0 |
| 2400 | 1 | 1 |