One of the most frustrating problems you can encounter is a faulty Ethernet cable. It doesn't happen often, but...
when it does it can waste a lot of your time. You can isolate this problem by tediously testing components until you isolate a single line.
Often you can solve the problem by checking and reseating the connection the Ethernet cable makes -- but not always. And unlike your network interface card (NIC), which you can PING, there really isn't any way you can address an Ethernet cable using software.
You need a hardware tool that you can use to test an Ethernet cable's condition. Ethernet cables are too expensive to simply toss every time you have a question.
Several companies make Ethernet cable testers, and you can even make one of these devices yourself for a small amount of money. Cables n More, for example, sells a $49 LAN Tester that can be used to check whether a cable is properly wired and operational. This device tests for thin Ethernet (bnc cable), 10BASET, rj1, rj2, and DEC cable. A master and remote device can test lengths up to 1000 feet. An article entitled "Build Your Own Cat5 Cable Tester" describes how to do this in some detail. (Editor's Note: If you are not into assembly language programming and mechanical assembly, this is for information only.)
Barrie Sosinsky is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.