THE CCNP EXAM TOPICS COVERED IN THIS
CHAPTER INCLUDE THE FOLLOWING:
Verify network connectivity.
Use the optimal troubleshooting approach in resolving
network problems.
Minimize downtime during troubleshooting.
Use Cisco IOS commands to identify problems.
Determine the layer or layers on which a problem is occurring.
As you know, to successfully troubleshoot network problems, it is
important to have a good understanding of how network components,
including PCs and servers, communicate with each other.
Without this basic knowledge, troubleshooting a network problem is like trying to read a book in
a foreign language. The information is there, but it just isn’t comprehensible. Although the troubleshooting
model discussed in Chapter 33, “Troubleshooting Methodology,” provides the method of
retrieving all the necessary information, the data is useless without an understanding of the information
presented.
This chapter is a review of the protocols used by layers 2, 3, and 4 of the OSI model. We briefly
review the seven layers of the OSI model, and then discuss how they communicate with one another.
We then discuss layer 2 and layer 3 protocols. More specific information on some of the material
covered here can be found in later chapters and is cross-referenced here where appropriate.
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