On a Cisco router, which command should you use to save the current running configuration in RAM to NVRAM so that it is preserved across reloads?

Introduction / Context:
This question examines your knowledge of how to save configuration changes on a Cisco router so that they are not lost when the device reboots. Administrators often modify settings in the running configuration and must then explicitly copy those changes to the startup configuration stored in Nonvolatile RAM.

Given Data / Assumptions:
- You have made changes to the router configuration in RAM (the running configuration).
- You want these settings to be retained after a reload or power cycle.
- Cisco IOS separates running-config (in RAM) and startup-config (in NVRAM).
- The question asks for the command that copies the running configuration into NVRAM.

Concept / Approach:
On Cisco routers, the command copy running-config startup-config (often abbreviated copy run start) is used in privileged EXEC mode to save the current running configuration to the startup configuration file in NVRAM. This ensures that when the router boots, it loads the saved configuration. Confusing this direction or using the wrong source and destination can lead to loss of changes or overwriting of the desired configuration.

Step-by-Step Solution:
Step 1: Confirm that you are in privileged EXEC mode, where the prompt ends with #.Step 2: Use the full command copy running-config startup-config or its accepted abbreviation copy run start.Step 3: When prompted, press Enter to accept the default source and destination filenames, unless you want to override them.Step 4: Wait for the router to confirm that the copy operation is successful.Step 5: Recognize that copy starting to running would merge startup into running, not the other way around, and that other sample options are not valid IOS syntax.

Verification / Alternative check:
After executing copy run start, you can reload the router or compare the startup and running configurations with show startup-config and show running-config. If the settings match, the save was successful. In many real environments, administrators also schedule regular backups of the configuration to external servers using copy running-config tftp for extra safety.

Why Other Options Are Wrong:
The command copy current to starting is not valid IOS syntax. The option copy starting to running does the reverse of what is required; it takes the configuration from NVRAM and merges it into RAM. The long form copy running-config startup-config is syntactically correct but is shown in global configuration prompt formatting in the option, which is misleading, whereas the question emphasizes the shorthand used in privileged EXEC mode. write erase would clear the configuration altogether, which is the opposite of saving it.

Common Pitfalls:
A common mistake is to forget to save changes at all, leading to configuration loss when the router reloads. Another is to accidentally copy startup-config to running-config after making changes, overwriting work in progress. Understanding the direction implied by copy source destination, and remembering that run start saves changes, helps avoid these issues.

Final Answer:
You should use the command Router#copy run start to save the running configuration in RAM to NVRAM as the startup configuration.