Troubleshooting Approaches
Divide and conquer

When you apply the divide-and-conquer approach toward troubleshooting a networking problem, you select a layer and test in both directions from the starting layer. Begin the divide-and-conquer approach at a particular layer based on the user experience level and the symptoms that have been gathered about the problem. The Cisco IOS command set allows the user to choose an intermediate level at which to begin troubleshooting and a direction to work toward. Once the direction of the problem has been identified, work in that direction until you can identify the cause of the problem.

If you can verify that a layer is functioning properly, it is typically a safe assumption that the layers below it are functioning. If a layer is not functioning properly, gather symptoms of the problem at that layer and work your way down.