- In a normal configuration, straight-through Ethernet cables are used; these have exactly the same pinout configuration on each end. Each end of the cable uses pins one and two to transmit, and pins three and six to receive. This means the switch or router device has to perform the crossover function of turning the signal around, so the signal goes out through the proper channels to the computers, which are all wired the same way: a signal from computer 'A' goes out through pins one and two to the router, which takes that signal and sends it to computer 'B' through pins three and six. Without this intervening function, 'A' and 'B' would be trying to send information to each other over pins one and two, and listening to pins three and six, so no communication would happen. A crossover cable swaps these pairs so that the wires that come from pins one and two on one end go to pins three and six on the other end. This means that while connected with the crossover cable, the two computers can communicate.
- To make a crossover cable, you will need a length of CAT5 or CAT6 cable, RJ45 ends, wire cutters and strippers, and an end crimper. There are two different wiring standards that use different colored pairs in different positions. For the purpose of a crossover cable, it doesn't matter which color the pair is, as long as you follow the same instructions. Strip back about an inch of insulation from the CAT5 cable. Separate the wires and untwist the pairs back to the insulation only. Organize them in the order of the standard you have chosen to use.
- The most common configuration is one pair on pins one and two like the white/orange pair, and one pair on pins three and six like the white/green pair. Four and five are usually the white/blue pair and seven eight are the white/brown pair. On one end, they will follow this color scheme and on the other, the white/orange pair will be on the three and six pins. The white/green pair will be on the one and two pins. No matter what colors you use, connect the one, two, three and six pins from one side to the three, six, one and two pins on the other in that order. Make sure the wires are fully inserted in the RJ45 plugs and crimp tightly twice until connected. Now you should be able to connect two computers directly through the Ethernet ports.
