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Chapter 7
Managing a Cisco Internetwork
Router#sh ver
[output cut]
Configuration register is 0x2102 (will be 0x0101 at next
reload)
Notice that the show version command shows the current configuration
register value, as well as what it will be when the router reboots. Any change
to the configuration register will not take effect until the router is reloaded.
The 0x0101 will load the IOS from ROM the next time the router is reboo-
ted. You may see it listed as 0x101, which is the same thing and can be
written either way.
Recovering Passwords
If you are locked out of a router because you forgot the password, you can
change the configuration register to help you recover. As noted earlier, bit 6
in the configuration register is used to tell the router whether to use the con-
tents of NVRAM to load a router configuration.
The default configuration register value is 0x2102, which means that bit 6
is off. With the default setting, the router will look for and load a router con-
figuration stored in NVRAM (startup-config). To recover a password, you
need to turn on bit 6, which will tell the router to ignore the NVRAM con-
tents. The configuration register value to turn on bit 6 is 0x2142.
Here are the main steps to password recovery:
1.
Boot the router and interrupt the boot sequence by performing a break.
2.
Change the configuration register to turn on bit 6 (with the value
0x2142).
3.
Reload the router.
4.
Enter privileged mode.
5.
Copy the startup-config file to running-config.
6.
Change the password.
7.
Reset the configuration register to the default value.
8.
Save the router configuration.
9.
Reload the router.
These steps are discussed in more detail in the following sections, showing
the commands to restore access to 2600 and 2500 series routers.
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