Cheap Networking Troubleshooter: Loopback Plug

A loopback plug can be very useful in testing and troubleshooting network problems. The loopback plug will cause the link light on a device, (a network card, switch, router, etc.) to come on. This is a very quick and cheap way to test simple network cabling problems. To make a loopback plug you just need to connect the transmit and receive lines together. (See picture.) Of course if you have some money to throw around you could buy a network tester a little bit more advanced, Fluke Networks offers a wide range of portable network testing equipment.