In this guide
An Ethernet crossover cable is a cable wired with T568A on one end and T568B on the other, crossing the transmit and receive pairs so two similar devices — like two computers or two switches — can communicate directly without a router or hub in between.
- Connecting two similar devices directly (PC-to-PC, switch-to-switch)
- Your devices do not support auto MDI-X
- Running a legacy or temporary network without a hub or router
- Connecting dissimilar devices like a PC to a switch — use a straight-through cable instead
- Both devices support auto MDI-X, which makes the cable redundant or may cause issues
- The wiring does not follow the correct T568A/T568B swap at each end
How the wiring works
A standard straight-through Ethernet cable uses the same wiring order — T568B — on both ends. A crossover cable uses T568A on one end and T568B on the other. This swap crosses pairs 2 and 3, routing the transmit (Tx) pins of one device into the receive (Rx) pins of the other.
Without this cross, two identical devices would both try to transmit on the same wire and receive on the same wire — and no data would get through. The crossover cable solves that problem in hardware. You can read more technical detail on the Ethernet crossover cable Wikipedia page.
When you actually need one
Crossover cables were common in the early 2000s for small office and home setups. Typical use cases included:
- Linking two PCs directly to share files or play LAN games
- Connecting two unmanaged switches to extend a network
- Cascading two routers without an uplink port
If you are setting up a direct device-to-device connection and neither device lists auto MDI-X support in its specs, a crossover cable is the right choice.
Do modern devices still need one?
Most network hardware made after 2005 includes auto MDI-X, which detects the cable type and adjusts the pin assignment automatically. This means a standard straight-through cable works fine even between two similar devices. Check your device’s manual or spec sheet — if auto MDI-X is listed, you do not need a crossover cable.
Gigabit Ethernet (1000BASE-T) uses all four wire pairs and requires auto MDI-X by specification, so crossover cables are effectively obsolete for modern Gigabit setups.
Quick compatibility table
| Setup | Works? | Need | Note |
|---|---|---|---|
| PC to PC (no auto MDI-X) | Yes | Crossover cable | Classic direct connection |
| Switch to switch (no auto MDI-X) | Yes | Crossover cable | Use uplink port if available |
| PC to switch | Yes | Straight-through cable | Crossover will fail here |
| Any devices with auto MDI-X | Yes | Either cable | Auto MDI-X corrects the signal |
| Gigabit devices | Yes | Straight-through cable | Crossover not required at 1 Gbps |
If you are troubleshooting a connection that uses video or display signals over modern connectors, you may also find our guides on whether USB-C can connect to HDMI and why USB-C to HDMI stops working useful for other cable compatibility questions.
Bottom line: An Ethernet crossover cable crosses the transmit and receive wire pairs to let two similar devices talk directly. It was essential before auto MDI-X became standard, but most modern hardware handles the correction automatically. If you are buying cable today for a Gigabit or newer network, a straight-through cable is almost certainly all you need — save the crossover cable for legacy hardware or very specific direct-connect scenarios.