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Sams Teach Yourself Network Troubleshooting in 24 Hours, Second Edition by Jonathan Feldman

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Diving into Details

As we discussed in Hour 2, it can be quite useful to consider pertinent layers of the OSI model. When thinking of where to start on a network problem, go through the useful OSI layers again: physical, data link, network, and application. Rule out problems, in order, because each progressive layer depends on the one before it. If there’s a physical problem, the data link isn’t going to work; but if the network is working, it’s a good guess that the data link is also okay.

To your users, everything is application oriented. That’s the nature of the beast: If users can’t get their apps, “the network is down.” But not every situation is as clear-cut as “down” versus “not down.” “I can’t get to the Foo application” usually implies ...

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