What Is an Ethernet Crossover Cable, and When Should You Use One?

The one time it's OK to cross the streams.

An Ethernet crossover cable swaps the transmit and receive pins between its plugs to allow for direct connections between host devices. Modern devices don't need this anymore, but older network devices might.

You probably don't think much about compatibility when you plug in your Ethernet cables, but sometimes when you directly connect two devices with an Ethernet cable, they won't talk to each other! This is where you need a "crossover" cable.

In a crossover cable, as opposed to a "straight through" cable, the transmit (TX) pin on one end of the cable has been connected to the receive (RX) pin. In other words, the signal traveling from one pin to another crosses over from the transmission and reception pins and vice versa.

Related: What Kind of Ethernet (Cat5, Cat5e, Cat6, Cat6a) Cable Should I Use?

Why? Because this allows two devices connected by Ethernet to talk directly to each other without needing a network switch, hub, or router between them. If you connect a straight-through cable to two host devices (such as two PCs) then both devices will try to transmit data packets on the same wire, and both will be listening on the same wire, so no actual data will make it through either way.

Geeks of a certain age will remember just how prized and useful crossover cables were before home Wi-Fi or network hubs that mere mortals could afford became commonplace. Crossover cables were great for sharing a dial-up internet connection between two PCs, for multiplayer gaming between two players, or for transferring files between computers much more quickly than using CDs, floppies, or even external hard drives.

A cheap, fast, and reliable way to turn on Ethernet cable from your router into seven.

You can still do that today, but with high-speed Wi-Fi, routers with integrated Ethernet ports, Powerline Ethernet, and incredibly cheap Ethernet switches, it doesn't seem worth the hassle.

However, there are still plenty of modern uses for crossover cables:

This isn't an exhaustive list, just a few examples to show you where these cables are helpful.

You can simply buy a pre-made crossover cable if you need one, but if you want to make one of the exact length you need, the classic way of making a crossover cable is to use a crimping tool. This tool lets you arrange the wires from an Ethernet cable as you wish and then crimps and seals them into an Ethernet plug.

A versatile crimping, stripping, and cutting tool that supports standard and pass-thru RJ4 plugs.

That being said, these days, it's far easier to buy a pair of crossover adapters. These little gadgets go onto the ends of an existing straight-through cable and convert them to crossover. Easy-peasy, with no wire stripping or swearing required.

They turn your standard Ethernet cable into a crossover cable for ten bucks.

Here's the real kicker: you probably don't need a crossover cable for direct connections. At least, you don't if your network gear is fairly recent. That's thanks to a feature known as "auto-MDIX" (Automatic Medium-Dependent Interface Crossover) and it allows any device to detect what sort of cable is plugged into it.

The computer, router, or whatever Ethernet device you've plugged into will figure out that you've plugged in a straight or crossover cable and then reconfigure the roles of the pins in its Ethernet port to allow for regular network communication.

If you have older network gear, there's absolutely still a need for crossover cables, but before you spend any money, try a direct connection with the Ethernet cables you already have to see if they work. The worst that can happen is that no data gets through; you can't damage anything this way.

Sydney Butler is a technology writer with over 20 years of experience as a freelance PC technician and system builder. He's worked for more than a decade in user education. On How-To Geek, he focuses on creating commerce content with simple buying advice and carefully chosen product suggestions.Sydney started working as a freelance computer technician around the age of 13, before which he was in charge of running the computer center for his school. (He also ran LAN gaming tournaments when the teachers weren't looking!) His interests include VR, PC, Mac, gaming, 3D printing, consumer electronics, the web, and privacy.He holds a Master of Arts degree in Research Psychology with a minor in media and technology studies. His masters dissertation examined the potential for social media to spread misinformation.