Monday at 1600. The only person authorized to use the
LAN after 1600 is PO1 Brush, who is the network
administrator. You call PO1 Brush and ask if any
changes were made to the word processing program
since yesterday. PO1 Brush states he installed a new
version of the word processing program on Monday
around 2200 to eliminate any work disruptions. You ask
him to check the security access to this new version.
You find PO1 Brush inadvertently restricted all users
from accessing the new version of the word processing
program after he removed the old one. He makes the
necessary access changes, and everybody is once again
happy and able to use the new version.
As you can see, there is a pattern to the various types
of errors/problems you will encounter. The problems
you will be confronted with will range from the simple
to the disastrous. They may be user/operator errors,
software problems, or hardware malfunctions.
Knowing which is sometimes easy. Under other
conditions, it may be difficult for you to determine the
source of the problem. The important thing is to learn
from your past experiences. Keep a list of symptoms,
probable causes, and ways you can use to trace a
problem to its cause. This will assist you in diagnosing
and troubleshooting problems. You will also find users
have a tendency to make the same mistakes again and
again, especially while they are learning. You can
provide them a great service by explaining some of the
more common problems they are likely to encounter,
the reasons for the problems, and ways to avoid having
them happen to them.
Any malfunction of the network is going to result in
a nonavailability of the system to the users. The
diagnosis and fixing of this malfunction becomes a high
priority. There are three primary culprits to network
malfunctions: component and server failures, and data
Component failures are categorized in two
categories: hard faults and soft faults. Hard faults are
relatively easy to find, and a diagnostic program will
diagnose them correctly every time. Soft faults can be
difficult to find, because they occur sporadically or only
under specific circumstances, rather than every time the
memory location is tested. A diagnostic program tests
computer hardware and peripheral devices for correct
Most computers run a simple set of system checks
when the computer is turned on. The PC tests are stored
in read-only memory (ROM), and are known as power-
on self tests (POSTs). If a POST detects an error
condition, the computer will stop and display an error
on the screen. Some computers will emit a beep signal
to indicate the type of error.
One of the best tools to use for network
malfunctions is a network analyzer. A network analyzer
is a product that can be used to monitor the activity of a
network and the stations on it, and to provide daily
summaries or long-term trends of network usage and
performance. A network analyzer can do tasks such as:
Count or filter network traffic.
Analyze network activity involving specified
protocols or frame structures.
Generate, display, and print statistics about
network activity, either as they are being
generated or in summary form.
Send alarms to a network supervisor or network
management program if any of the statistics
being monitored exceeds predetermined limits.
Do trend or pattern analyses of network activity.
Network analyzers may be software only or consist
of both software and hardware. The latter may include
an interface card enabling you to test the network
directly. This card may include an on-board processor.
Because of their greater capabilities, hardware/software
analyzers are more expensive than the software only
analyzers. In fact, the prices for the hardware/software
analyzers can be several times as high as those for the
software only versions.
The most obvious sign that the server has failed for
some reason is that all users, except root, will not be able
to logon to the system. Use the following steps as
required to reestablish services:
The first and easiest thing to try is to run the
system distribution again. This will rebuild the
system maps if nothing else is wrong and will
allow users access to the system.
Shutdown and reboot the system. During the
boot process ensure that no failures occur on any
of the nodes.