[B][Interrupting the Router Boot Sequence[/B]
Your first step is to boot the router and perform a break. This is usually done by pressing the
Ctrl+Break key combination when using HyperTerminal and while the router first reboots.
The Windows NT or 2000 default HyperTerminal program won’t perform the
break. You’ve got to upgrade the HyperTerminal program or use Windows 95/
98 instead.
After you’ve performed a break, you should see something like this:
System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
Copyright (c) 1999 by cisco Systems, Inc.
TAC:Home:SW:IOS:Specials for info
PC = 0xfff0a530, Vector = 0x500, SP = 0x680127b0
C2600 platform with 32768 Kbytes of main memory
PC = 0xfff0a530, Vector = 0x500, SP = 0x80004374
monitor: command "boot" aborted due to user interrupt
rommon 1 >
Notice the line "boot" aborted due to user interrupt. At this point, you will be at the
rommon 1> prompt on some routers.
Changing the Configuration Register
As I explained earlier, you can change the configuration register by using the config-register
command. To turn on bit 6, use the configuration register value 0x2142.
Remember that if you change the configuration register to 0x2142, then the
startup-config will be bypassed and the router will load into setup mode.
Cisco 2600 Series Commands
To change the bit value on a Cisco 2600 series router, you just enter the command at the rommon
1> prompt:
rommon 1 > confreg 0x2142
You must reset or power cycle for new config to take effect
Cisco 2500 Series Commands
To change the configuration register on a 2500 series router, type o after creating a break
sequence on the router. This brings up a menu of configuration register option settings. To
change the configuration register, enter the command o/r, followed by the new register value.
Here’s an example of turning on bit 6 on a 2501 router:
System Bootstrap, Version 11.0(10c), SOFTWARE
Copyright (c) 1986-1996 by cisco Systems
2500 processor with 14336 Kbytes of main memory
Abort at 0x1098FEC (PC)
>o
Configuration register = 0x2102 at last boot
Bit# Configuration register option settings:
15 Diagnostic mode disabled
14 IP broadcasts do not have network numbers
13 Boot default ROM software if network boot fails
12-11 Console speed is 9600 baud
10 IP broadcasts with ones
08 Break disabled
07 OEM disabled
06 Ignore configuration disabled
03-00 Boot file is cisco2-2500 (or 'boot system' command)
>o/r 0x2142
Notice that the last entry in the router output is 03-00. This tells the router what the IOS
boot file is. By default, the router will use the first file found in the flash memory, so if you want
to boot a different file name, you can either change the configuration register or use the boot
system ios_name command.
Reloading the Router and Entering Privileged Mode
At this point, you need to reset the router like this:
From the 2600 series router, type reset.
From the 2500 series router, type I (for initialize).
The router will reload and ask if you want to use setup mode (because no startup-config is
used). Answer No to entering setup mode, press Enter to go into user mode, and then type
enable to go into privileged mode.
Viewing and Changing the Configuration
Now you’re past the point where you would need to enter the user mode and privileged mode
passwords in a router. Copy the startup-config file to the running-config file:
copy startup-config running-config
or use the shortcut:
copy start run
The configuration is now running in random access memory (RAM), and you’re in privileged
mode, meaning that you can now view and change the configuration. But you can’t view the
enable secret setting for the password. To change the password, do this:
config t
enable secret todd
Resetting the Configuration Register and Reloading the Router
After you’re finished changing passwords, set the configuration register back to the default
value with the config-register command:
config t
config-register 0x2102
Finally, save the new configuration with a copy running-config startup-config and
reload the router.