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isco equipment functions in accordance with the OSI model.

Routers are known as Layer 3--Network devices. Cisco has developed many
ways to efficiently and effectively move incoming data to the correct out-
bound interface. These methods are described in detail in this chapter.

Because different applications use different packet sizes, it is important to

gain an understanding of the buffers implemented by Cisco and how they
can be configured to provide more efficient use of memory buffers. Buffer
configuration is also addressed in this chapter.

Armed with the general information regarding protocols and troubleshoot-

ing tools, you're ready to cover Cisco-specific material. This chapter discusses
the output of Cisco diagnostic commands, and Cisco-specific routing and
switching procedures.

Understanding the Output from Diagnostic
Commands

efore an engineer can effectively and successfully troubleshoot network

problems, they need to understand the processes being analyzed. If this under-
standing is not present, then information provided by troubleshooting tools is
useless. Troubleshooting is like learning another language--if you don't have a
basic vocabulary and knowledge of the jargon, you can't pick up a book written
in a foreign language and understand it. Troubleshooting is similar--if you don't
understand the technology and processes present in the problems you trouble-
shoot, diagnostic information is of little use. This section is dedicated to a discus-
sion of the processes that occur on Cisco routers.

Several processes exist simultaneously on a router, and it is important to

single out which processes are of interest. Sometimes diagnostic tools can
affect available resources on the router. Not only can resources be used, but
the efficiency with which routers handle packets may also be affected.

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