Make a Crossover Ethernet Cable

RJ45 Connector This guide is a DIY to create a crossover ethernet cable. While a normal ethernet cable is used to connect a PC to a router / modem / network, a crossover cable can be used to enable direct communication between two computers. This is a very low cost solution to enable communication between two computers directly without the need of intermediate hardware. It is for file sharing, LAN gaming and controlling remote computers.

A normal ethernet cable allows only one way data transmissions while a crossover cable allows both way data transmission.
This is achieved by connecting the transmission pins (TX+ & TX-) of one end to the receiving pins(RX+ & RX-) of the other end. In a normal ethernet cable, this is done internally by the hub / switch or the router.

In a normal RJ45 / CAT5 ethernet cable, the pins are marked as 1. TX+, 2. TX-, 3. RX+, 6. RX- at both ends. To create a crossover ethernet cable we just connect the TX pins to the corresponding RX pins. In effect, we swap wires at the pins 1-3 and 2-6.

In a normal ethernet cable,
We have the following pin configuration at both ends:

1: TX+
2: TX-
3: RX+
6: RX-

Crossover Wire layout While in a crossover cable, we have:

Crossover
1: TX+ <—-> 3: RX+
2: TX- <—-> 6: RX-
3: RX+ <—-> 1: TX+
6: RX- <—-> 2: TX-

We let the Pins 4,5,7,8 remain unaltered.

To make a crossover cable, you need:

A standard RJ45 / CAT5 ethernet cable

RJ45 connectors for both ends.

Ethernet Connector Just take of the connectors, if already present, from one end of the ethernet cable. Strip off some wire from the open end and arrange the wires, swapped as explained earlier. Just insert them in the spare RJ45 connector and connect them to the pins properly. Just apply some force on the connector and it should click into place. You can also use a crimper to attach the RJ45 connector to the other end tightly.

At this stage your crossover cable is complete and you are all set to create your own small sharing network. Frag on!

Notes:
1. The maximum length of RJ45 ethernet cables is limited to 100M in theory and a lot lesser than that in reality. If the distance is longer than that, you may need to use repeaters.
2. Make sure that the cable is not twisted at any point.