What is the purpose of a loopback test in troubleshooting?

The purpose of a loopback test in troubleshooting is to verify local device functionality. This type of test involves sending a signal from a device and routing it back into the device itself, bypassing the network. By doing so, it allows technicians to check that the device's internal components, such as the network interface card (NIC), are operating correctly and that it can send and receive data without external interference.

Loopback tests are commonly used to diagnose issues like defective ports or problems with the device's firmware or drivers. By confirming that the local equipment is functioning as intended, further troubleshooting can then be targeted towards other issues, such as network configuration or external connectivity, if problems persist after the loopback test. This ability to isolate local issues from external factors is what makes the loopback test an essential tool in the troubleshooting process.

The other options focus on aspects like measuring speeds or checking external connectivity, which do not directly relate to the primary function of a loopback test, as it is specifically oriented towards ensuring that the device itself is operational.