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“One of these things is not like the other!” This popular children’s exercise can certainly come into play with our various troubleshooting approaches!
When you engage in the The Spot the Differences approach to troubleshooting, you attempt to compare functioning to malfunctioning devices or processes and spot the differences. This might even allow you to implement a solution or a workaround to a problem without even understanding the underlying cause.
By comparing configurations, software versions, hardware or link properties between working and nonworking situations and spotting significant differences between them, you might be able to resolve the problem by changing the nonoperational situation to be consistent with the working situation.
As alluded to above, the biggest disadvantage with this method is that it can lead to a working situation, but not to an understanding of the root cause of the problem.
You should notice that the effectiveness of this method depends on how easy it is to compare working and nonworking devices, situations, or processes. Having a good baseline of what constitutes normal behavior on the network makes it easier to spot abnormal behavior. Also, the use of consistent configuration templates makes it easier to spot the significant differences between functioning and malfunctioning devices. As a result of all of these factors, the effectiveness of this method does typically depend on the quality of the overall network maintenance process.
Finally, you should also take note that like the follow-the-path method, this approach is best used as a supporting method in combination with other methods such as top-down or bottom-up troubleshooting.
Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
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