15.1 Introduction to Troubleshooting


Troubleshooting can best be described as the process of finding the root cause of a system problem by methodically working from a broad spectrum of possibilities and narrowing them down to a final solution. Most network engineers have some personalized method of troubleshooting that they instinctively use whenever a problem occurs. Some prefer to look at the big picture ”how broad is the problem, which remote sites are being affected, and so forth. Some engineers like to keep a knowledge base of information about past network outages so they can do quick searches for relevant information. Some engineers , of course, use a combination. Troubleshooting can be described as both an art and a science, using proven scientific methods in a uniquely personal way to achieve the fastest , best result.

Many engineers prefer to use the bottom-up philosophy based on the OSI network model (refer to Figure 2-1 and its accompanying text for a review of the OSI model). By using Layers 1 through 3 ”physical, data link, and network ”the engineer can dissect and analyze a problem in a methodical fashion.

Using this model, the engineer would first assess the physical layer of the network, asking the following questions:

  • Is everything connected physically?

  • Are there any utility outages, such as a fiber cut?

  • Are all indicators normal?

  • Are there any active alarms?

The next step would be to assess the link layer, or Layer 2, indicators for framing errors, transmit and receive errors, and so on. Finally, Layer 3, the network layer, is where the engineer could gather information necessary for understanding the routing information that is being passed or received by the router. Using this model, each layer represents another way of analyzing the problem until all methods have been exhausted or until the problem is found and resolved.

Another troubleshooting method many engineers use involves finding out what, if any, changes were made in the network since it was last known to be stable. Then, the method is to work backwards from the current situation until reaching the point at which the network restabilizes. Sometimes a software upgrade is found to be the cause of the problem. More often, though, a configuration change is the root cause.

Regardless of the method used, the goal is to get the network running smoothly again as quickly as possible. The JTAC prescribes a tried-and-true troubleshooting method for networks using their routers. The following sections discuss this troubleshooting methodology, describe trouble indicators, and introduce hardware troubleshooting commands.



Juniper Networks Reference Guide. JUNOS Routing, Configuration, and Architecture
Juniper Networks Reference Guide: JUNOS Routing, Configuration, and Architecture: JUNOS Routing, Configuration, and Architecture
ISBN: 0201775921
EAN: 2147483647
Year: 2002
Pages: 176

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net