Cisco Certified Network Associate (CCNA) Practice Exam

How can you confirm the proper WAN protocol encapsulation on a serial interface?

1. debug ip nat

2. show interface serial

3. show ip interface brief

4. copy run start

The correct answer is: show interface serial

To confirm the proper WAN protocol encapsulation on a serial interface, using the command to display interface details is most effective. The command `show interface serial` provides comprehensive information about the serial interface, including its status, protocol, and encapsulation type. This command reveals critical details such as whether the interface is up or down, the encapsulation being used (e.g., PPP, HDLC), and the specific statistics related to the interface's performance. By analyzing this output, you can ascertain whether the encapsulation is set correctly for the desired WAN protocol. In contrast, the other commands serve different purposes. For example, the command to display interface status provides a quick summary of all interfaces but does not give detailed encapsulation information. Meanwhile, the NAT debug command pertains specifically to Network Address Translation activities, and the command to copy the running configuration to startup configuration is related to saving configurations rather than providing specific interface data. Therefore, when confirming WAN protocol encapsulation, the command that gives detailed status and protocol information for the serial interface is the most appropriate choice.