There are three main methods for troubleshooting networks:
- Bottom up
- Top down
- Divide and conquer
Each approach has its advantages and disadvantages
Bottom-Up Troubleshooting Method
In bottom-up troubleshooting you start with the physical components of the network and move up through the layers of the OSI model until the cause of the problem is identified. Bottom-up troubleshooting is a good approach to use when the problem is suspected to be a physical one. Most networking problems reside at the lower levels, so implementing the bottom-up approach often results in effective results. The figure shows the bottom-up approach to troubleshooting.
The disadvantage with the bottom-up troubleshooting approach is it requires that you check every device and interface on the network until the possible cause of the problem is found
In bottom-up troubleshooting you start with the physical components of the network and move up through the layers of the OSI model until the cause of the problem is identified. Bottom-up troubleshooting is a good approach to use when the problem is suspected to be a physical one. Most networking problems reside at the lower levels, so implementing the bottom-up approach often results in effective results. The figure shows the bottom-up approach to troubleshooting.
The disadvantage with the bottom-up troubleshooting approach is it requires that you check every device and interface on the network until the possible cause of the problem is found
Top-Down Troubleshooting Method
In top-down troubleshooting your start with the end-user applications and move down through the layers of the OSI model until the cause of the problem has been identified. End-user applications of an end system are tested before tackling the more specific networking pieces. Use this approach for simpler problems or when you think the problem is with a piece of software.
The disadvantage with the top-down approach is it requires checking every network application until the possible cause of the problem is found.
In top-down troubleshooting your start with the end-user applications and move down through the layers of the OSI model until the cause of the problem has been identified. End-user applications of an end system are tested before tackling the more specific networking pieces. Use this approach for simpler problems or when you think the problem is with a piece of software.
The disadvantage with the top-down approach is it requires checking every network application until the possible cause of the problem is found.
Divide-and-Conquer Troubleshooting Method
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.
In divide-and-conquer troubleshooting you start by collecting user experience of the problem, document the symptoms and then, using that information, make an informed guess as to which OSI layer to start your investigation. Once you verify that a layer is functioning properly, assume that the layers below it are functioning and work up the OSI layers. If an OSI layer is not functioning properly, work your way down the OSI layer model.
For example, if users can't access the web server and you can ping the server, then you know that the problem is above Layer 3. If you can't ping the server, then you know the problem is likely at a lower OSI layer.
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.
In divide-and-conquer troubleshooting you start by collecting user experience of the problem, document the symptoms and then, using that information, make an informed guess as to which OSI layer to start your investigation. Once you verify that a layer is functioning properly, assume that the layers below it are functioning and work up the OSI layers. If an OSI layer is not functioning properly, work your way down the OSI layer model.
For example, if users can't access the web server and you can ping the server, then you know that the problem is above Layer 3. If you can't ping the server, then you know the problem is likely at a lower OSI layer.
Questioning End Users
When you question end users about a network problem they may be experiencing, use effective questioning techniques. This way you will get the information you need to effectively document the symptoms of a problem. The table in the figure provides some guidelines and end-user example questions.
When you question end users about a network problem they may be experiencing, use effective questioning techniques. This way you will get the information you need to effectively document the symptoms of a problem. The table in the figure provides some guidelines and end-user example questions.
NMS Tools
Network management system (NMS) tools include device-level monitoring, configuration, and fault management tools. The figure shows an example display from the What's Up Gold NMS software. These tools can be used to investigate and correct network problems. Network monitoring software graphically displays a physical view of network devices, allowing network managers to monitor remote devices without actually physically checking them. Device management software provides dynamic status, statistics, and configuration information for switched products. Examples of commonly used network management tools are CiscoView, HP Openview, Solar Winds, and What's Up Gold.
Network management system (NMS) tools include device-level monitoring, configuration, and fault management tools. The figure shows an example display from the What's Up Gold NMS software. These tools can be used to investigate and correct network problems. Network monitoring software graphically displays a physical view of network devices, allowing network managers to monitor remote devices without actually physically checking them. Device management software provides dynamic status, statistics, and configuration information for switched products. Examples of commonly used network management tools are CiscoView, HP Openview, Solar Winds, and What's Up Gold.
Physical Layer Troubleshooting
Data Link Layer Troubleshooting
Network Layer Troubleshooting
Transport Layer Troubleshooting
Application Layer Troubleshooting
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