The cable that you will need to use is called cross-over cable. It is different from a regular cable, called pin-to-pin cable.

Twisted pair networking cables have eigth wires divided into four pairs and are usually assembled using a pin-to-pin configuration, where the position of the pair of wires is the same on both ends of the cable. I.e. the position of the wires is the same for both ends of the cable.

On Fast Ethernet networking cards (a.k.a. 100BaseT or 100 Mbps networking cards) one pair is used for transmitting data and another pair is used for receiving data. The other two pairs are left unused.

Connecting two computers using a pin-to-pin cable doesn’t work because with this cable you will connect the transmitting pair of one computer to the transmitting pair of the other computer (instead of the receiving pair) and the receiving pair of the first computer to the receiving pair of the other computer (instead of the transmitting pair). Thus it is impossible to the two computers to talk to each other.

In order to connect computers using pin-to-pin connectors you need an extra device, like a hub or a switch. What a hub or a switch does is to “cross” these two pair, making the transmitting pair of the first computer to be connected to the receiving pair from the other computer, and the receiving pair from the first computer to be connected to the transmitting pair of the other computer. This way the communication can be established.

A cross-over cable is a regular twisted pair networking cable that connects the transmitting pair of the first computer to the receiving pair from the other computer and vice-versa, thus allowing the communication to be established. It is called cross-over because it crosses these two pairs instead of using a pin-to-pin connection.

So, what is different about this cable isn’t its material, wires or connector. It is just a regular twisted pair networking cable with its wires connected differently at one of its ends.

You can buy this cable already assembled or your can build it by yourself, if you have the skills.

On Figure 1 you can see a cross-over cable. The cable itself is just a regular twisted pair networking cable. Its color is irrelevant.

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Figure 1: A cross-over cable.

The trick is at one of the connectors. If you compare both connectors, you will see that the order of the wires at one connector is different from the other (each wire has a different color). On a regular pin-to-pin cable, both connectors use the same wire order.

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Figure 2: The order of the wires is different, thus indicating that this is a cross-over cable (compare the position of orange and green wires).

If you want to build this cable by yourself, we present the wire order on the table below.

Pin (Connector A)	Wire Color	Pin (Connector B)
1	White with green stripe	3
2	Green	6
3	White with orange stripe	1
4	Blue	4
5	White with blue stripe	5
6	Orange	2
7	White with brown stripe	7
8	Brown	8

The table above is for 100 Mbps networks. If you want to build a Gigabit Ethernet (1000BaseT) cross-over cable, you will need to follow the order presented on the table below (you will also need to use a Cat5e cable). This happens because Gigabit Ethernet uses two pairs for transmitting data and two pairs for receiving data.

Pin (Connector A)	Wire Color	Pin (Connector B)
1	White with green stripe	3
2	Green	6
3	White with orange stripe	1
4	Blue	7
5	White with blue stripe	8
6	Orange	2
7	White with brown stripe	4
8	Brown	5