Cisco Certified Network Associate (CCNA) Practice Exam 2025 - Free CCNA Practice Questions and Study Guide

To enable an interface in configuration mode, the command utilized is "no shutdown." This command is critical in Cisco devices because, by default, most interfaces are administratively shut down when initially configured. When an interface is administratively down, it cannot send or receive any packets.

By executing "no shutdown," you instruct the device to activate that specific interface, allowing it to begin functioning and become capable of transmitting data across the network. This command is essential for network engineers and administrators, as it is a fundamental step in setting up the network interfaces necessary for connectivity.

The other choices do not serve this specific function. For instance, "enable" is used to transition from user mode to privileged exec mode on a Cisco device, while "start" and "activate" are not valid commands for enabling interfaces in Cisco IOS configuration. Therefore, using "no shutdown" is the correct approach when you want to activate an interface in a Cisco network device configuration.