As the name implies, when you use the
bottom-up troubleshooting
approach, you start with the
bottom—the Physical layer of the OSI model—and work your way up to the top—the Application
layer. This approach is used when you suspect the problem is at the Physical layer, or when you
are troubleshooting a complex network problem. In these situations, ensuring that the core components
required for networking are in place can go a long way toward isolating the problem.
The downside to bottom-up troubleshooting is that it can require the checking of each interface
along the path to see if errors are occurring there. Depending on the length of the path from
the end points of the problem, this process can be very time-consuming. In these cases, determining
the most likely culprit based on the symptoms of the trouble can save a lot of time.