This is a list of some of the less well known / used commands, that we often overlook that are still nevertheless very useful. This is an ongoing list that I hope to grow as I come across / learn new one or remember old ones. If you can think of any please let me know.
If you use the #copy running-config startup-config, you will know that the device will replace the config stored in NVRAM. However the other way round #copy start run, the saved configuration is merged with the running configuration. This can lead to inconsistencies or configuration left in place because there is not saved part of the configuration to over write it. The configure replace command will remove the running configuration and replace it completely with configuration contained in the named file. Can be very useful when you want to undo a change you have made to the running configuration, allowing you to revert to the startup configuration with out having to preform a reboot.
This is a great command to use when changing configuration on a device remotely. You can use it to set a countdown timer which when expired the device will reboot. Set it to reboot in 10 minutes, apply you configuration. If all goes well cancel the timer using #reload cancel. But if something goes wrong and you lose connection, wait for the timer to expire, the device reloads and the startup configuration is reapplied. Just be sure not to save the configuration before you are sure all is working correctly. And make sure you remember to cancel the timer before it runs out!
router#reload at time
Another useful command to allow you to reload a switch at a specified time, I often use this after an IOS upgrade. Once I know that a new IOS works, I will often do the copying and setting up during the day, and end with specifying a reload command that is out of hours. No having to stay late or come in out of hours. Just make user you can monitor that it has come back up OK before the users get back in!!
<Ctrl> + <Shift> + 6 togather followed by x (aborts / suspend)
Ctrl-R (refreshes screen)
Router#U all (undebug all)
This is a much simpler command to type when you debug command has resulted in you terminal window getting filled with never ending output.