What is the running-config?

The running-config refers to the current active configuration that a Cisco device, such as a router or a switch, is using at any given moment. This configuration is stored in the device's RAM and reflects all the changes that have been made to the network device since it was last powered on or rebooted.

Any modifications made to the device’s settings, such as interface configurations, routing protocols, and access control lists, are applied to the running-config immediately. This is crucial because it allows network administrators to implement and test new settings dynamically without needing to restart the device or load a new configuration from storage.

It’s important to note that changes in the running-config are temporary; if the device is rebooted or powered off, this configuration will be lost unless it has been saved to the startup-config, which is stored in NVRAM. Hence, understanding the distinction between running-config and startup-config is key for managing network devices efficiently.