A crossover cable swaps the transmit and receive wire pairs between its two ends, letting two similar devices talk directly. A straight-through cable keeps the same wiring on both ends and is used for connecting different devices — like a PC to a switch.
- You’re linking two similar devices directly (PC-to-PC, switch-to-switch)
- Your gear does not support Auto MDI-X
- You use a crossover cable between a PC and a switch or router without Auto MDI-X
- You need a straight-through connection but only have a crossover cable and no Auto MDI-X support
What is the difference?
A straight-through cable uses the same wiring standard (T568B) on both RJ45 ends. Pins 1-2 carry transmit signals on one device and land on the receive pins of a different type of device — the switch or router handles the flip internally.
A crossover cable uses T568A on one end and T568B on the other. This physically swaps pins 1-2 with pins 3-6, reversing the TX and RX pairs. When two identical devices connect, neither flips the signal automatically, so the cable does the job instead.
When to use each cable
| Setup | Works? | Need | Note |
|---|---|---|---|
| PC to switch/router | Yes | Straight-through | Standard home/office setup |
| PC to PC (direct) | Yes | Crossover | No switch needed |
| Switch to switch | Yes | Crossover | Use uplink port if available |
| Modern gear (Auto MDI-X) | Yes | Either | Port auto-negotiates TX/RX |
| PC to switch with crossover | No | Straight-through | Fails without Auto MDI-X |
Auto MDI-X makes crossover cables mostly obsolete
Most network hardware made after 2000 includes Auto MDI-X, a feature that detects the cable type and adjusts TX/RX automatically. If your switch, router, or NIC supports it, you can plug in either cable type and the link will come up. Check your device spec sheet if you’re unsure.
According to StarTech’s cable reference guide, Auto MDI-X is now standard on virtually all Gigabit Ethernet ports, making crossover cables a niche item for older or industrial equipment.
How to identify which cable you have
- Hold both RJ45 ends side by side, clip facing away from you
- If the wire colour order is identical on both ends — it’s straight-through
- If the order differs (notably positions 1-2 vs 3-6) — it’s a crossover
- Some crossover cables are labelled or colour-coded by the manufacturer
If you’re also troubleshooting other cable types, our guide on why USB-C to HDMI is not working covers similar signal-direction issues in a different context. For video over USB-C specifically, see our explainer on whether USB-C supports video output.
Bottom line: Use a crossover cable only when directly connecting two identical devices on older hardware without Auto MDI-X. For everything else — PC to switch, PC to router, or any modern Gigabit port — a standard straight-through cable is the right choice, and Auto MDI-X will handle the rest automatically.