Troubleshooting any sort of network problem should follow a systematic approach. Logical networking models, such as the OSI and TCP/IP models, separate network functionality into modular layers.
When troubleshooting, these layered models can be applied to the physical network to isolate network problems. For example, if the symptoms suggest a physical connection problem, the network technician can focus on troubleshooting the circuit that operates at the physical layer. If that circuit functions properly, the technician looks at areas in another layer that could be causing the problem.
There are three main troubleshooting approaches used to resolve network problems:
- Bottom-up - Start at Layer 1 and work up. (Figure 1)
- Top-down - Start at the top layer and work down. (Figure 2)
- Divide-and-conquer - Ping the destination. If the pings fail, verify the lower layers. If the pings are successful, verify the upper layers. (Figure 3)