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Chabot College. ELEC 99.08 Password Recovery. Password Recovery Topics. Problem: Lost Password Overview & Strategy Step-by-Step. Problem: Lost Password. If line passwords are lost, you can’t log on. If enable secret is lost, you can’t do anything useful.

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chabot college
Chabot College

ELEC 99.08

Password Recovery

password recovery topics
Password Recovery Topics
  • Problem: Lost Password
  • Overview & Strategy
  • Step-by-Step
problem lost password
Problem: Lost Password
  • If line passwords are lost, you can’t log on.
  • If enable secret is lost, you can’t do anything useful.
  • Unless you can recover from this situation, your router’s config can never be changed. For all practical purposes, the router is a doorstop.
overview strategy
Overview & Strategy
  • 3 ways to “recover”
    • view the password oak#show run
    • change the password oak(config)#enable secret chabot
    • erase the configuration, including the password, and start overoak#erase startoak#reload
  • To do any of these, which mode must you be in?


overview strategy5
Overview & Strategy
  • To enter privileged mode, what is usually required?

enable secret password

  • So that’s the key to the strategy:Enter the privileged mode without knowing the enable secret!
  • Here’s how...
overview strategy6
Overview & Strategy
  • Configure the router to start up without reading its configuration file. (that’s where the passwords are stored)
  • Do this by
    • interrupting the normal boot process
    • setting the config-register to ignore the config file
    • rebooting the router (again)
  • When it reboots, it has no config and no passwords. Just enable the privileged mode!
  • Change, view, or erase the passwords.
  • Restore the config register for a normal boot.
step by step 1
Step-by-Step: 1
  • Connect to the router’s console port.
step by step 2
Step-by-Step: 2
  • Display and record the current value of the router’s config register. You’ll need to reset the register to this value later, so write it down now.

show version

If you can’t login to the router, you can discover the setting in a later step.

oak>show version

Cisco Internetwork Operating System Software IOS (tm) 2500 Software (C2500-JS-L), Version 12.0(7)T, RELEASE SOFTWARE

16384K bytes of processor board System flash (Read ONLY) Configuration register is 0x2102

step by step 3
Step-by-Step: 3
  • Power-cycle the router
  • Why can’t you use reload?
  • What mode must you be in to reload?


What must you know to be able to enter the privileged mode?

enable secret

so, you must use the power switch...

step by step 310
Step-by-Step: 3
  • Power-cycle the router
  • Within 60 seconds, interrupt the normal boot process:
    • Press break key (control-break on Hyperterm PE)
    • The router enters ROM-monitor mode and presents this prompt >

!-- The router was just powercycled !-- During bootup a break sequence was sent to the router. !

Abort at 0x10EA83C (PC)


step by step option if step 2 could not be performed
Step-by-Step (option if Step 2 could not be performed)
  • Display and record the current value of the router’s config register. You’ll need to reset the register to this value later, so write it down now.


Letter “o”,

not the number zero

Abort at 0x10EA83C (PC)

>oConfiguration register = 0x2102 at last boot Bit# Configuration register option settings:...

step by step 4
Step-by-Step: 4
  • Set the config register to ignore the config file during boot:

>o/r 0x2142

4 here causes

config file not

to be loaded

Letter “o”,

not the number zero

Abort at 0x10EA83C (PC)

>o/r 0x2142

step by step 5
Step-by-Step: 5
  • Reboot the router (again):



(The router reboots, but ignores its config file.)

Abort at 0x10EA83C (PC)

>o/r 0x2142 >i

step by step 6
Step-by-Step: 6
  • Do not enter the system config dialog.(Use control-C to skip all questions.)


--- System Configuration Dialog --- Would you like to enter the initial configuration dialog? [yes/no]:


step by step 7
Step-by-Step: 7
  • Enable the privileged mode


  • No password is required, because the router has not loaded a configuration file.
  • This is the key step. Now you can do whatever you want!


step by step 8
Step-by-Step: 8
  • Load the config file by copying the startup config to the running config:

copy start run

  • It’s OK to load the config now - you’re already in privileged mode!

Router#Router#copy start runoak#

step by step 9
Step-by-Step: 9
  • View the running config:

show run

  • You can now see all passwords except the enable secret! (it is encrypted, so you’ll need to change it.)

oak#oak#show run

step by step 10
Step-by-Step: 10
  • Change the enable secret:

conf t

enable secret [word]

  • Now you’re all set.

oak#oak#conf toak(config)#enable secret chabot

step by step 11
Step-by-Step: 11
  • Restore the original setting of the configuration register:

config-register 0x2102

  • This step causes the router to load its config file normally at next reboot.

oak#oak#conf toak(config)#config-register 0x2102

step by step 12
Step-by-Step: 12
  • Bring up all interfaces that are in use:

no shut

  • The interfaces were administratively shut down when the router booted with no config file.

oak#(config)#int e0oak(config-if)#no shutoak(config-if)#int s0oak(config-if)#no shutoak(config-if)#int s0oak(config-if)#no shut

step by step 13
Step-by-Step: 13
  • Save the current config-register setting to NVRAM, and then reboot:

copy run start


oak#conf toak(config)#config-register 0x2102oak(config)^Zoak#copy run startoak#reload

  • So…
  • Why should Cisco routers be kept in physically secure areas, where the general public can’t get access to the console port?