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Troubleshooting: The OSI model

Troubleshooting a customer's temperamental network is a tough job made even tougher if you don't have a strategy. An organized methodology for troubleshooting will not only make a VAR's search for the source of a network's problems more effective, but also much quicker. Here we look at some tips for router troubleshooting success, including the OSI layered model.

Troubleshooting a customer's temperamental network is a tough job made even tougher if you don't have a strategy. An organized methodology for troubleshooting will not only make a VAR's search for the source of a network's problems more effective, but also much quicker. In this tip we look at some tips for router troubleshooting success, including the OSI layered model.

Troubleshooting routing: Strategies for fast problem solving

Typically, when someone mentions a methodology, we think of something like the scientific method, which we might alter a bit for our purposes. Thus, we might go through some distinct phases in our troubleshooting where we would first prepare by understanding the normal, steady-state operation. Then, when the trouble occurs, we would define the problem, based on symptoms (e.g. "the network is slow" or "I cannot connect to the VAX"). Next, we'd identify the current state of the network, performing steps such as checking to see if the WAN circuits are up or collecting device logs as appropriate. Finally, we'd form a hypothesis and test it.

This sort of methodical process as it's weaknesses in router troubleshooting. Primarily, it can be exceedingly slow as it turns over and examines every stone in the search for the source of the problem. Additionally, it doesn't account for the natural learning process, where a VAR or consultant will learn from previous experience and apply it to future challenges.

Despite these failings, however, the most detailed strategies are often the most effective. The trick is finding which methodology works for you. One popular set of methodologies is the seven layered OSI model.

The OSI Model's layers:

  • Application
  • Presentation
  • Session
  • Transport
  • Network
  • Data-link
  • Physical

Learn more about the OSI model and other router troubleshooting methodologies.

About the author
Tom Lancaster, CCIE# 8829 CNX# 1105, is a consultant with 15 years experience in the networking industry, and co-author of several books on networking, most recently,
CCSPTM: Secure PIX and Secure VPN Study Guide published by Sybex.

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