router#show version | Last line of output tells you what the configuration register is set to | router#config t | | router(config)#config-register 0x2142 | Changes the configuration register to 2142 |
The Configuration Register: A Visual Representation The configuration register is a 16-bit eld stored in NVRAM. The bits are numbered from 15 to 0 looking at the bit stream from left to right. Bits are split up into groups of 4, and each group is represented by a hexadecimal digit. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| Bit places | 0 0 1 0 0 0 0 1 0 1 0 0 0 0 1 0
| Register bits | 2 1 4 2
| Bits represented in hex |
The Configuration RegisterWhat the Bits Mean Bit Number | Hexadecimal | Meaning |
---|
0003 | 0x0000 0x000F | Boot Field | 06 | 0x0040 | Ignore NVRAM contents | 07 | 0x0080 | OEM bit enabled | 08 | 0x0100 | Break disabled | 09 | 0x0200 | Cause system to use secondary bootstrap (typically not used) | 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 and ignores NVRAM contents |
The Boot Field Note: Even though there are 16 possible combinations in the boot field, there are only three that are used. Boot Field | Meaning |
---|
00 | Stays at the ROM Monitor on a reload or power cycle | 01 | Boots the first image in Flash memory as a system image | 02 F | Enables default booting from Flash memory Enables boot system commands that override default booting from Flash memory |
Tip: Because the default boot field has 14 different ways to represent it, a configuration register setting of 0x2102 is the same as 0x2109, or 210F. The boot system command is described in Chapter 16, "Backing Up and Restoring Cisco IOS Software and Configuration." Console Terminal Baud Rate Settings Baud | Bit 5 | Bit 12 | Bit 11 |
---|
115200 | 1 | 1 | 1 | 57600 | 1 | 1 | 0 | 38400 | 1 | 0 | 1 | 19200 | 1 | 0 | 0 | 9600 | 0 | 0 | 0 | 4800 | 0 | 0 | 1 | 2400 | 0 | 1 | 1 | 1200 | 0 | 1 | 0 |
Changing the Console Line SpeedCLI router#config t | | router(config)#line console 0 | Enters console line mode | router(config-line)#speed 19200 | Changes speed to 19200 baud |
Tip: Cisco IOS software does not allow you to change the console speed bits directly with the config-register command. Changing the Console Line SpeedROM Monitor Mode1700/2600 Series rommon1>confreg | Shows configuration summary. Step through the questions, answering with the defaults until you can change the console baud rate | Configuration Summary enabled are: load rom after netboot fails console baud: 9600 boot: image specified by the boot system commands or default to: x (name of system image) do you wish to change the configuration? y/n [n]: y enable "diagonstic mode"? y/n [n]: n enable "use net in IP bcast address"? y/n [n]: n disable "load rom after netboot fails"? y/n [n]: n enable "use all zero broadcast"? y/n [n]: n enable "break/abort has effect"? y/n [n]: n enable "ignore system config info"? y/n [n]: n change console baud rate? y/n [n]: y enter rate: 0=9600, 1=4800, 2=1200, 3=2400 4=19200, 5=38400, 6=57600, 7=115200 [0]: 7
| | Configuration Summary enabled are: load rom after netboot fails console baud: 115200 boot: image specified by the boot system commands or default to: x (name of system image)
| | change the boot characteristics? y/n [n]: n | After the summary is shown again, choose n to not change the configuration and go to the rommon> prompt again | rommon2> | |
Tip: Make sure that after you change the console baud rate, you change your terminal program to match the same rate! |