When a connectivity issue occurs, which stage in troubleshooting involves checking various network layers?

The stage in troubleshooting that involves checking various network layers is the divide-and-conquer approach. This methodology is effective because it allows the technician to isolate and narrow down the potential causes of a connectivity issue in a systematic manner. In troubleshooting, especially in networking, problems can be complex and scattered across different layers, such as the physical, data link, network, transport, and application layers.

By using the divide-and-conquer strategy, you can test each layer independently to identify where the issue lies. For example, you might first check the physical layer to ensure cables are connected and operational. If everything there appears to be functioning, you would then move up to the data link layer, and so forth, examining each layer until the root cause of the problem is identified.

This method contrasts with other approaches, such as top-down or bottom-up strategies, which focus on starting the troubleshooting process from either the application layer downwards or the physical layer upwards, without necessarily addressing middle layers effectively. Network verification is more about validating that the network configuration and devices are operating as intended rather than systematically isolating issues across layers. Therefore, using divide-and-conquer allows for a thorough examination of each layer, increasing the chances of efficiently diagnosing and resolving the connectivity issue.