Interpreting Visual Indicators

  • Given a network scenario, interpret visual indicators (e.g., link lights, collision lights) to determine the nature of the problem.

One of the first and easiest methods to spot signs of trouble on a network or with a network component is to look at the LEDs that appear on most network components. Many of the devices used in modern networks—such as hubs, routers, switches, and even NICs—have LEDs that let you know what, if anything, is going wrong. The following sections examine some of the common networking devices and what you can learn from their LEDs.


Software Versus Hardware Loopback Chapter 13, “Troubleshooting Connectivity ,” discusses the use of the local loopback address ( as a means of testing ...

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