Cisco Certified Network Associate (CCNA) Practice Exam

What is the command to enable an interface on a router?

1. (config-if)#enable

2. (config-if)#no shut

3. (config)#activate

4. (config-if)#start

The correct answer is: (config-if)#no shut

The command to enable an interface on a router is "no shut." This command is a shorthand for "no shutdown," and it is used within interface configuration mode. When an interface is created on a Cisco router, it is administratively shut down by default, which means it won't pass any traffic. By entering the "no shut" command, you are effectively activating the interface, allowing it to begin to process packets and become operational. The syntax of the command reflects Cisco’s command line interface (CLI) design, where "no" typically negates a command, and in this case, it negates the shutdown state. It is a standard practice in network configurations to ensure that all necessary interfaces are enabled properly for communication within a network. Other options provided do not correspond to valid commands for enabling an interface. For instance, options like "enable," "activate," and "start" do not exist in this context and would not effectively change the operational status of a router interface. Therefore, understanding the use of "no shut" is essential for anyone configuring routers in a Cisco environment.