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 on 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.