Setup Mode

We never use wizards/setup mode if we can avoid it; wizards may make assumptions and we want to see all the questions. Go through set-up mode and understand what it does. Then delete the router and start again! In the real world, we never use set-up mode and normally configure devices manually from the CLI.

  1. You should now be back at a set-up mode prompt. Answer no and press return to get started. Type enable to get to privileged mode.

  2. Type show run to see running-config.

  3. If you type show startup-config you will get a response startup-config is not present, because you have not yet saved a configuration.

  4. Type copy running-config startup-config and then check again for the startup-config.

  5. If you now type reload, the router will come up with the new start-up configuration.

  6. You can delete the startup-conf file by typing the command erase startup-config. If you now do a reload, you are back to having an un-configured switch/router.

The Configuration Register

You should now be back at a set-up mode prompt. Answer no and press return to get started.

  1. Type enable to get to privileged mode.

  2. Type show run to see running-config.

  3. If you type show startup-config you will get a response startup-config is not present, because you have not yet saved a configuration.

  4. Type copy running-config startup-config and then check again for the startup-config. All CISCO routers have a 16-bit configuration register which we can use to repair, recover or hack a router! Download and browse “Use of the Configuration Register on All Cisco Routers” Cisco Document ID 50421. Document and understand the meanings of each bit in the register, you will need this!

  5. Use show version command to document the current value of the configuration register. The default value for this register is 0x2102. Never proceed without documenting the actual value, do not assume it is the default!!

  6. Understand how to set the Configuration Register from Configuration Mode. You now can change how the router boots and runs.

  7. Using the techniques above, change the value of the Configuration Register to 0x2101 and reload. You should load a small version of IOS from ROM rather than the one on the flash drive. Look for a message similar to the one below.

System returned to ROM by power-on
System image file is "c2800nm-advipservicesk9-mz.124-15.T1.bin"

  1. When you finish, restore the Configuration Register to its original value and reload.

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