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Chapter 12
Troubleshooting Network Problems
As with your car, the best defense against problems is prevention. Just as you should have
your car serviced regularly, so you should monitor the health of your network regularly.
Of course, even the most well-monitored network will sometimes experience unexpected problems. For example, a utility company could dig a new hole for its cable and
accidentally cut your dedicated line to the Internet. In such a situation, your network
can go from perfect to disastrous performance in an instant. In this chapter, you learn
how to diagnose and solve network problems in a logical, step-by-step fashion, using a
variety of tools.
TROUBLESHOOTING METHODOLOGY
Successful troubleshooters proceed logically and methodically.This section introduces a
basic troubleshooting methodology, leading you through a series of general problemsolving steps. Bear in mind that experience in your network environment may prompt
you to follow the steps in a different order or to skip certain steps entirely. For example, if you know that one segment of your network is poorly cabled, you may try replacing a section of cable in that area to solve a connectivity problem before attempting to
verify the physical and logical integrity of the workstation’s NIC. In general, however,
it is best to follow each step in the order shown. Such a logical approach can save you
from undertaking wasteful, time-consuming efforts such as unnecessary software or
hardware replacements.
Steps for troubleshooting network problems are as follows:
1. Identify the symptoms. Carefully document what you learn from people or
systems that alerted you to the problem and keep that documentation handy.
2. Identify the scope of the problem. Is it universal—that is, are all users on the
network experiencing the problem at all times? Or is the problem limited to
a specific geographic area of the network, to a specific demographic group of
users, or to a particular period of time? In other words, is the problem subject
to geographic, demographic, or chronological constraints?
3. Establish what has changed on the network. Recent hardware or software
changes may be causing the symptoms.
4. Determine the most probable cause of the problem. This determination may
include the following techniques:
a. Verify user competency.
b. Re-create the problem, and ensure that you can reproduce it reliably.
c. Verify the physical integrity of the network connection (such as cable connections, NIC installations, and power to devices), starting at the affected
nodes and moving outward toward the backbone.
d. Verify the logical integrity of the network connection (such as addressing,
protocol bindings, software installations, and so on).