A Cisco IOS router stores configurations in two locations – RAM and NVRAM. The running configuration is stored in RAM and is used by the router during operation. Any configuration changes to the router are made to the running-configuration and take effect immediately after the command is entered. The startup-configuration is saved in NVRAM and is loaded into the router’s running-configuration when the router boots up. If a router loses power or is reloaded, changes to the running configuration will be lost unless they are saved to the startup-configuration. To save the running-configuration to the startup configuration, type the following from privileged EXEC mode (i.e. at the “Router#” prompt.)
Router# copy running-config startup-config
Note: Prior to 11.x software, the command to save the running-configuration to the startup-configuration was different. Use the following command if your IOS version is prior to 11.x:
IMPORTANT: When editing a configuration, SAVE the configuration often!