System information

CHAPTER
Troubleshooting Overview 1-3
1
Troubleshooting Overview
Internetworks come in a variety of topologies and levels of complexity—from single-protocol,
point-to-point links connecting cross-town campuses, to highly meshed, large-scale wide-area
networks (WANs) traversing multiple time zones and international boundaries. The industry trend is
toward increasingly complex environments, involving multiple media types, multiple protocols, and
often interconnection to “unknown” networks. Unknown networks may be defined as a transit
network belonging to a Internet service provider (ISP) or a telco that interconnects your private
networks. In these unknown networks, you do not have control of such factors as delay, media types,
or vendor hardware.
More complex network environments mean that the potential for connectivity and performance
problems in internetworks is high, and the source of problems is often elusive.The keys to
maintaining a problem-free network environment, as well as maintaining the ability to isolate and
fix a network fault quickly, are documentation, planning, and communication. This requires a
framework of procedures and personnel to be in place long before any network changes take place.
The goal of this book is to help you isolate and resolve the most common connectivity and
performance problems in your network environment.
Symptoms, Problems, and Solutions
Failures in internetworks are characterized by certain symptoms. These symptoms might be general
(such as clients being unable to access specific servers) or more specific (routes not in routing table).
Each symptom can be traced to one or more problems or causes by using specific troubleshooting
tools and techniques. Once identified, each problem can be remedied by implementing a solution
consisting of a series of actions.
This book describes how to define symptoms, identify problems, and implement solutions in generic
environments. You should always apply the specific context in which you are troubleshooting to
determine how to detect symptoms and diagnose problems for your specific environment.
General Problem-Solving Model
When you’re troubleshooting a network environment, a systematic approach works best. Define the
specific symptoms, identify all potential problems that could be causing the symptoms, and then
systematically eliminate each potential problem (from most likely to least likely) until the symptoms
disappear.
Figure 1-1 illustrates the process flow for the general problem-solving model. This process flow is
not a rigid outline for troubleshooting an internetwork; it is a foundation from which you can build
a problem-solving process to suit your particular environment.