How to Build a Network Using a Cross-Over Cable
By Gabriel Torres on March 2, 2007


Introduction

You can build a small network between two computers using a very cheap networking cable, called cross-over cable. This can be a terrific solution if you are looking for an inexpensive way of putting together only two computers for allowing them to share files, printers and Internet access. In this tutorial we will teach you in details how this can be done.

You will need, however, two network cards installed on one of the computers. The first card will be connected to your broadband modem and the other card will be used to connect this computer to the other computer, through a cross-over cable (this cable can be bought already assembled or you can build it by yourself). This is why some high-end motherboards have two on-board network cards: they allow you to share your Internet connection without needing to install a broadband router, by installing one of the ports to your broadband modem and the other to the other computer.

Of course if you don’t have or don’t want broadband Internet access you won’t need two network cards on one of the computers. So dial-up users will need only one network card at each computer. Another situation you could build this simple network without Internet access is when you want to connect two computers just for copying files, like copying all files located on your hard drive to another computer, for example.

The extra card on the computer that has the broadband Internet connection and a cross-over cable is all you will need to build a network using two computers.

You need to keep in mind, however, that this kind of network has some limitations:

You are able to connect the two computers without using any extra device because you will be using a special networking cable, not a regular one. So let’s talk about this cable.

Cross-Over Cable

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.

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

Cross-Over Cable
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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.

Cross-Over Cable
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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 in 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 in 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

Installation

The installation of this kind of network is very simple. First you will need to install a second network card on the computer that has your broadband Internet connection. Some high-end motherboards have already two on-board network cards, allowing you to build this kind of network without needing to buy and install a second card. In Figure 3 we show the detail of a motherboard with such feature.

Dual Network Ports
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Figure 3: Example of a high-end motherboard with two on-board network cards.

The second and final step is really simple: just connect each end of the cross-over cable to each computer and that’s it! Your network will be assembled!

If you want to connect more than two computers without using a router, you will need to connect a pin-to-pin cable (and not a cross-over one) to the computer that has your Internet connection and the other end of the cable to a hub or switch, and then all other computers to this hub or switch. The configuration procedure is the same.

But your network won’t be working. You will need to configure the operating system on the computer that has your broadband Internet connection (for simplicity let’s call it “host computer”). Basically what we will need to do is to share your Internet connection. The configuration of the other computer (let’s call it “client computer”) is really simple, as we will only need to tell it to use all configurations set by the host computer.

Let’s see how this needs to be done.

Configuring The Host Computer

Configuring a network using a cross-over cable on Windows XP and Vista is really simple, as these operating systems allow you to create your own network with just one mouse click.

On the computer that has your broadband Internet connection, go to Start, Control Panel, Network Connections. There you will see your two network cards being listed but one of them – the one that you connected your cross-over cable to – will be listed with a yellow exclamation mark, being described with “Limited or no connectivity” (see Figure 4). This is absolutely normal, as we haven’t set up our network yet.

Configuring Your Network
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Figure 4: The network cards on your host computer.

Right click the network card that is connected to your broadband modem (and not the card with the yellow exclamation mark) and, from the list that will show up, choose Properties. Then, on the window that will be opened, click on Advanced tab. There check the “Allow other network users to connect through this computer’s Internet connection” box and make sure to uncheck the “Allow other network users to control or disable the shared Internet connection”, see Figure 5. Click on Ok after doing this configuration. If you are sharing a dial-up connection, this procedure should be done at your dial-up connection.

Sharing Your Internet Access
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Figure 5: Sharing your Internet connection.

Your host computer is now correctly configured. As you can see in Figure 6, the second network card is now being shown as “Connected” and the network card that is connected to your broadband modem is now being listed with “Shared” on its properties.

Configuring Your Network
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Figure 6: Your network correctly configured and operational.

If you do not have broadband Internet access – i.e., you have just one network card installed on each computer – the procedure is different, as you won’t be able to share your Internet connection as you don’t have one. In this case the easiest way (in our opinion) to setup your network is by configuring it manually. This is done at the TCP/IP configuration settings of each computer, and we will show you how this is done in the next page.

Configuring The Client Computer

Now you need to configure the other computer to get its settings automatically from the network. This is really simple to do, as this is Windows’ default setting. However, it is always a good thing to double check whether your computer is correctly configured or not.

First go to Start, Control Panel, Network Connections. There you will see your network card and probably it will be listed with a yellow exclamation mark and being described with “Limited or no connectivity” (see Figure 7). This is normal to happen and we will fix this in just a second.

Configuring Your Network
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Figure 7: The network card on your client computer.

Right click the network card and, from the list that will show up, choose Properties. The window shown in Figure 8 will appear. There double click “Internet Protocol (TCP/IP)”.

Setting Up a Network
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Figure 8: Network card properties.

The window shown in Figure 9 will appear. There you need to check if “Obtain an IP address automatically” and “Obtain DNS server address automatically” options are selected.

Setting Up a Network
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Figure 9: TCP/IP properties.

After clicking Ok, your network card will probably still being listed as having “Limited or no connectivity” with a yellow exclamation mark, see Figures 7 and 10.

Configuring Your Own Network
Figure 10: Your network card isn’t connected yet.

Now you need to double click your network card (either on Network Connections or on its small icon on the task bar) and, on the window that will show up, click on Support tab (see Figure 11). There click on Repair button and your network connection will be automatically fixed.

Fixing Your Network
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Figure 11: Fixing your network connection.

After this procedure your network will be working. Try opening any website on your client computer to test it out.

If you want to share files and printers between your computers, read our tutorial How to Share Folders and Printers on Your Network.

If you do not have broadband Internet access – i.e., you have just one network card installed on each computer – you will need to manually configure the TCP/IP protocol. You should follow all the steps present on this page but when comes to configuring the TCP/IP protocol (Figure 9) you need to configure it manually instead of automatically.

At one of the computers, you should, on the screen present in Figure 9, configure your computer like this:

You should configure the other computer like this:

Originally at http://www.hardwaresecrets.com/article/How-to-Build-a-Network-Using-a-Cross-Over-Cable/426


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