Network Troubleshooting Methods

Troubleshooting Methods
There are three main methods for troubleshooting networks:
Bottom up
Top down
Divide and conquer
Each approach has its advantages and disadvantages. This topic describes the three methods and provides guidelines for choosing the best method for a specific situation.

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. Remember that each conclusion and possibility must be documented so there can be a lot of paper work associated with this approach. A further challenge is to determine which devices to start examining first.

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. Each conclusion and possibility must be documented. and the challenge is to determine which application to start examining first.

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.

Guidelines for Selecting a Troubleshooting Method
To quickly resolve network problems, take the time to select the most effective network troubleshooting method. Examine the figure. Use the process shown in the figure to help you select the most efficient troubleshooting method.
Here is an example of how you would choose a troubleshooting method for a specific problem. Two IP routers are not exchanging routing information. The last time this type of problem occurred it was a protocol issue. So you choose the divide-and-conquer troubleshooting method. Your analysis reveals that there is connectivity between the routers so you start your troubleshooting efforts at the physical or data link layer, confirm connectivity and begin testing the TCP/IP-related functions at next layer up in the OSI model, the network layer.


Post a Comment


NBA Live Streaming. Copyright 2008 All Rights Reserved Revolution Two Church theme by Brian Gardner Converted into Blogger Template by Bloganol dot com | Distributed by Blogger Templates Blog