On a Cisco router, which command copies the startup configuration file from nonvolatile memory into DRAM so that it becomes the running configuration?

Introduction / Context:
Cisco routers and switches maintain two main configuration files. The startup configuration is stored in nonvolatile Random Access Memory and is used when the device boots. The running configuration resides in Dynamic Random Access Memory and controls the current behaviour of the device. Many administrative tasks require copying configuration data from one location to another. This question focuses on the exact command that copies the startup configuration file into DRAM, effectively replacing or merging it with the running configuration.

Given Data / Assumptions:

• We are working on a Cisco IOS based router or switch.
• There is a valid startup configuration saved in nonvolatile memory.
• The administrator wants to load that saved configuration into DRAM as the running configuration.
• We assume access to privileged EXEC mode where copy commands are available.

Concept / Approach:
Cisco IOS uses the copy source destination syntax for moving configuration data. The most common operations are copying running-config to startup-config to save current settings permanently, and copying startup-config to running-config to restore a saved configuration into active memory. When a device boots, it automatically reads the startup-config into running-config. However, an administrator can manually repeat this action at any time without rebooting by issuing the correct copy command. This is frequently done after testing configuration changes and wanting to revert to the last saved version.

Step-by-Step Solution:
1. Identify the source file: the stored configuration in nonvolatile memory is called startup-config. 2. Identify the destination file: the active configuration file in DRAM is called running-config. 3. Apply the command syntax copy source destination, replacing source with startup-config and destination with running-config. 4. The resulting full command is copy startup-config running-config. 5. After executing this command in privileged EXEC mode, the router prompts for confirmation and then reads the saved configuration into the running configuration.

Verification / Alternative check:
After issuing copy startup-config running-config, you can use the show running-config command to confirm that the active configuration matches the expected saved configuration. Another check is to compare show startup-config and show running-config before and after the copy. In many cases, administrators perform this command when they have accidentally made unwanted changes in the running configuration and want to revert to the last saved state without restarting the device.

Why Other Options Are Wrong:
copy running-config startup-config: This command does the reverse operation. It saves the current active configuration into nonvolatile memory so that it is used at the next reload. It does not copy from startup to running.
copy nvram flash: This command would copy data from nonvolatile memory into flash storage, not into DRAM as the running configuration.
write erase: This command erases the startup configuration and is used when resetting a router to factory defaults. It does not copy anything into DRAM.
reload startup-config: There is no reload startup-config command in Cisco IOS. The reload command alone reboots the device, and the router then automatically loads startup-config, but this is not an immediate copy into DRAM without a reboot.

Common Pitfalls:
A frequent error is to mix up the direction of the copy command. Many new administrators intend to save changes permanently but accidentally use copy startup-config running-config, which instead restores old settings on top of new ones. Another mistake is to expect write memory to load configuration from nonvolatile memory, when in fact it saves the current running configuration. Always read the command from left to right as copy source to destination, and be very careful about which file is the source and which is the destination to avoid losing important configuration changes.

Final Answer:
copy startup-config running-config