If you have two or more computers equipped with wireless adapters (WiFi cards), it is possible to easily connect them in a network by setting up a so-called "ad hoc" network, that is, a computer-to-computer network, without using an access point.
Before doing anything else, you need to equip all the machines that will be on the future ad hoc network with a wireless adapter and install drivers.
A new icon appears in the taskbar, indicating the presence of an active wireless adapter in the computer:
By default, Windows XP offers a utility making it possible to configure wireless networks. The Microsoft Windows XP wireless network configuration utility disables manufacturer configuration tools. To disable the Windows XP tool, simply click Start/Settings/Network connections, then right-click the icon corresponding to the wireless network and choose Properties. In the wireless network configuration tab, check or uncheck Use Windows to configure my wireless network.
This manipulation involves enabling or disabling Windows XP's wireless network automatic configuration service. An alternative is to go to the control panel/Administrative tools/Services, and then to start or stop the Automatic wireless configuration service.
The properties dialogue box for the wireless network connection (wireless network configuration tab) presents the networks detected by the wireless adapter and lets you configure them.
To create an ad hoc network, you need to add a new network, identified by a unique name, the SSID. To do so, click the button Add. A new dialogue box opens:
To create the ad hoc network, on each of the future network's computers, you simply need to enter the same SSID and check the box "This is a computer-to-computer network". The other options are used to heighten security. Firstly, leave the network completely open (with the options in the above screenshot), so as not to multiply settings that could prevent the first networking.
If the icon on the taskbar shows a small cross, it means that the computer is not connected to the wireless network; you should check the following points:
The previous steps let you connect the various machines. However, to be able to fully use the network, you need to define an IP addressing for the network's machines and set up a certain number of services (web server, shared files, internet connection sharing, etc.).
For this type of network, it is necessary to use a private IP address. There are address ranges reserved to that effect, in this case 192.168.0.1 to 192.168.0.255 will be sufficient (or 192.168.1.1 to 192.168.1.255 if you already have a local network with the previous addressing).
If one of the computers on the ad hoc network already has an internet access it wants to share with the network's other computers, it is usually named 192.168.0.1 (or 192.168.1.1), but this is just a convention. The other machines will take addresses from the same address range: 192.168.0.2, etc.
To configure the machine, simply right-click the icon corresponding to the wireless network connection, then choose "properties":
Then, in the list of protocols, select "Internet protocol (TCP/IP)" and click "Properties":
Enter each machine's IP address, making sure not to enter the same IP address twice, 255.255.255.0 as subnet mask and possibly the IP address of the machine sharing the internet access (default gateway, with the address 192.168.0.1 by convention).
In the fields concerning the DNS, enter the IP addresses of the name servers corresponding to the connected machine's service provider. To find them out, you can just enter the following command for example (Start/Run) on the machine that's connected to the internet:
cmd /k ipconfig /all
All that's left is to test the connection between the machines on the ad hoc network.