Switch Password Recovery: The Configuration Register
The console wants a password nobody remembers. Interrupt the boot, bypass the saved configuration, and reset the passwords without losing it, live, right below.
Symptom
The console wants a password nobody knows. Interrupt the boot, make the switch ignore its saved configuration, then reset the passwords without losing anything.
Your mission
Prove the cause, then fix it
Format
Guided CLI investigation
Investigate before you configure.
Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.
Observe the symptom and link state.
Diagnose by comparing the protocol evidence.
Verify the expected device state and confirm the original symptom is resolved.
Console access: SW1
This workspace stacks for portrait phones. Rotate to landscape for the full split-screen console.
Need a hint?
Reveal the root cause when you're ready.
Try the investigation first, then use this as your escape hatch, not a dead end.
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Lab debrief
Turn the session into a repeatable troubleshooting pattern.
Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.
The problem
SW1 asks for a console password that nobody remembers, so there is no route to the enable prompt. The saved configuration is valuable and must survive, so erasing the switch is not an option.
What you'll practice
- Explain why a lost password does not need the configuration erased
- Interrupt the boot and pass the configuration register as a boot argument
- Recognise a switch that has deliberately ignored its startup-config
- Copy the startup-config into the running-config before changing anything
- Reset the register and save, and see what happens if you forget
The topology
One switch reached only through its console. There is no network path to it, which is why recovery has to happen at boot time rather than from a remote session.
Commands to run yourself
The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.
show version | include Configurationshow startup-config | include hostname|enable secret|passwordcopy startup-config running-configTopology diagram
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Frequently asked
Why does 0x2142 skip the saved configuration?
Bit 6 of the configuration register (0x0040) tells the switch to ignore the startup-config at boot. 0x2142 is the normal 0x2102 with that bit set. On this virtual switch the register reaches the system as the decimal boot argument confreg=8514.
What happens if I save with the register still at 0x2142?
The save also stores the register, so the next reload ignores the startup-config again and the switch boots empty. The lab shows this in its output. Setting config-register 0x2102 before you save is the step that stops it.
Is this how a physical Catalyst is recovered?
The idea is the same, but the boot interruption differs between platforms and models. This lab covers the procedure exactly as it works on the virtual IOSvL2 switch image, so check Cisco's procedure for your hardware before relying on it.
Ready to run this lab yourself?
No setup, no image sourcing. Book a session or ask for a live demo.