Cisco Certified Network Associate (CCNA) Practice Exam

The command that is used to test if a configured serial link can forward packets is "ping." This command sends Internet Control Message Protocol (ICMP) echo request messages to the target host, and if the serial link is operational and configured correctly, the target will send back an echo reply. This is a basic yet effective way to verify that the network path is functional and that the packets can reach their destination.

Using ping provides valuable feedback on packet loss, latency, and the accessibility of the serial link or device in question. When you ping an IP address associated with a serial connection, it helps ensure that the connection is capable of transmitting data, confirming the link is not only established but also fully operational for packet forwarding.

The other options do not directly accomplish this specific task. For instance, "test connection" and "check connectivity" are not standard commands found in Cisco IOS. The "traceroute" command allows you to see the path packets take to a destination and can indicate where failures occur, but it is not a straightforward test of whether a specific link can forward packets.