Methods for Making Router Changes
Most changes can be made and checked in the running (working) configuration file in RAM without affecting the startup configuration file.
If the changes made to the running-config file work, you can copy the running-config to startup-config using the copy run start command.
If the changes made to the running-config file don’t work, use the reload command or reboot the router by turning it off and on. This will load the startup configuration file into RAM again.
Remember, it is best to keep a copy of the clean configuration files on a TFTP server for backup purposes.