What does the command 'copy running startup' do?

The command 'copy running-config startup-config' (often abbreviated as 'copy running startup') is used in Cisco devices to save the current running configuration stored in RAM to the startup configuration stored in NVRAM. When you make configuration changes on a Cisco device, these changes are initially made in the RAM, which is volatile memory. If the device is rebooted or powered off, any changes not saved will be lost.

By executing this command, the running configuration, which includes all the current settings and configurations you have implemented, is written to NVRAM. This ensures that the configurations persist even after a reboot, allowing the device to resume operation with the desired settings the next time it is powered on.

Understanding this command is critical for network management, as it helps maintain configuration continuity and prevents loss of important settings.