Quick HOWTO : Ch04 : Simple Network Troubleshooting/zh

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Introduction

You will eventually find yourself trying to fix a network related problem which usually appears in one of two forms. The first is slow response times from the remote server, and the second is a complete lack of connectivity. These symptoms can be caused by:


Sources of Network Slowness

  • NIC duplex and speed incompatibilities
  • Network congestion
  • Poor routing
  • Bad cabling
  • Electrical interference
  • An overloaded server at the remote end of the connection
  • Misconfigured DNS (Covered in Chapter 18, "Configuring DNS" and Chapter 19, "Dynamic DNS")

Sources of a Lack of Connectivity

All sources of slowness can become so severe that connectivity is lost. Additional sources of disconnections are:

  • Power failures
  • The remote server or an application on the remote server being shut down.

We discuss how to isolate these problems and more in the following sections.

Doing Basic Cable and Link Tests

Your server won't be able to communicate with any other device on your network unless the NIC's "link" light is on. This indicates that the connection between your server and the switch/router is functioning correctly.

In most cases a lack of link is due to the wrong cable type being used. As described in Chapter 2, "Introduction to Networking", there are two types of Ethernet cables crossover and straight-through. Always make sure you are using the correct type.

Other sources of link failure include:

  • The cables are bad.
  • The switch or router to which the server is connected is powered down.
  • The cables aren't plugged in properly.

If you have an extensive network, investment in a battery-operated cable tester for basic connectivity testing is invaluable. More sophisticated models in the market will be able to tell you the approximate location of a cable break and whether an Ethernet cable is too long to be used.