Do you need a crossover cable?

If you want to connect two computers directly via their Ethernet ports, you could use something called a crossover cable – but you may not have to.

A crossover cable takes the output of one end of the cable and connects it to the input of the other. If you were using an Ethernet switch or hub, the crossing over would happen within that device. However, if you don’t want to bother with introducing that external device, with its power requirements, you can use a crossover cable. Another use for the cable would be to connect two hubs together.

The term “crossover cable” is a bit generic, but in general it refers to copper-based, twisted-pair Ethernet cables. So this would include Category-5, Category-5E and Category-6 cabling. The “normal” version is a straight-through cable, but a crossover makes the change from input to output.

These cables are available for purchase, but you could also potentially make one yourself. Sites like this one spell out how to connect the wires within the cable to the correct pinouts on the RJ-45 connectors to do the crossover.

This site spells out how you would configure two PCs running Windows 98 and above to talk to each other once a crossover cable is in place.

Now, the need for crossover cables has been eliminated with more modern equipment. Gigabit Ethernet was created with a widely used option called Auto-MDIX (automatic medium-dependent interface crossover). This technology detects whether you need a crossover cable or a straight-through cable, and it automatically configures the network interface card accordingly.

Thanks to this technology, if you are using Gigabit Ethernet, chances are you will be able to connect your PCs or hubs with regular, straight-through cables, and the NICs on either end will detect the cable and adjust accordingly.

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