Windows Client Configuration
Windows Server 2003 and Windows XP make it easy to configure a client to use wireless networks, especially networks that use WEP. Microsoft introduced the Wireless Zero Configuration service in XP and called it the Wireless Configuration service in Windows 2003. When running, the service monitors wireless NICs for reception of SSID broadcasts from APs. If a broadcast with a known SSID is received and enough configuration information is available, Windows can automatically join the wireless network if configured to do so. The wireless configuration service also gives you a standard dialog box interface for configuring wireless network settings regardless of the wireless NIC installed. Unfortunately, the service doesn't work with all wireless NICs; if it doesn't work with yours, you'll need to disable it and use the driver and configuration toolset that came with your NIC.
To use the configuration service, open the Network Connections Control Panel applet, right-click the wireless NIC item, select Properties, and go to the Wireless Networks tab. Make sure that the Use Windows to configure my wireless network settings option is selected, and click Add to configure a wireless network. Figure 1 shows the dialog box that lets you enter details for a wireless network. Enter the SSID for the wireless network you want to connect to, then select a method for Network Authentication. If you select Open or Shared, your options for the Data encryption field are WEP or Disabled. If you select WPA or WPA-PSK, your data encryption options are TKIP or AES.
When using WEP or WPA-PSK for authentication or encryption, you can enter the authentication or encryption key (to enable the Network key field and Confirm network key field, you'll need to clear the option The key is provided for me automatically). If you have more than one key, select the key number, or index. Some APs and wireless NICs let you store and use up to four keys for flexibility. You might rotate keys weekly, for example, manually selecting the next key on the list each Monday morning.
Locating Rogue APs
As mentioned earlier, rogue APs can present untold risk to the enterprise. But the benefits that an AP can offer plus the ease of installation (especially installation that just uses the default configuration settings) make it highly likely that somewhere, sometime, someone will deploy one on your network.
Finding rogue APs can be problematic but is necessary to maintain effective security. Windows 2003 has a new Microsoft Management Console (MMC) snap-in called Wireless Network Monitor that you can use to log network client activity and to find APs. However, installing Windows 2003 on a laptop just for an MMC snap-in is cumbersome, expensive, and unnecessary. Most laptops and PDAs with built-in wireless NICs come with tools that can be used to detect rogue APs.
If your laptop or PDA doesn't come with such a tool or if you want advanced features such as GPS support (which when used with a directional antenna and a compass lets you triangulate the location of a rogue AP), then you might find a freeware tool such as NetStumbler preferable. Two versions are available from http://www.netstumbler.com/
downloads: one for Windows 2000 and later and one for Windows CEbased devices, called MiniStumbler. Figure 2 shows NetStumbler running on a Dell laptop that has XP Service Pack 2 (SP2) and a Dell TrueMobile 1400 wireless NIC, one of many wireless NICs supported by NetStumbler.
You can use NetStumbler to locate rogue APs simply by running it on a laptop and walking around with the laptop. As NetStumbler detects APs, it displays them on the screen. It provides information such as the AP's MAC address, channel that it listens on, whether encryption is in use, and vendor information. NetStumbler also shows the signal-to-noise ratio (SNR) for the radio signal. The higher the number, the closer you are to the AP.
Before you can detect rogue APs, you need to know the MAC address and SSID of each legitimate AP in use in your enterprise. As you deploy APs, record their MAC address, their SSID, and where you've placed them. As you walk around with NetStumbler, look for APs that have an unfamiliar SSID or an unknown MAC address. As you find them, record your location, then walk in different directions and note in which direction the SNR number increases. If you keep walking in that direction, you'll eventually come across the AP or at least determine the general area in which it's located for a more thorough physical examination at a later date. Don't forget that an AP could actually be located on a floor above or below you.
Be particularly aware that a sophisticated hacker might establish an AP with the same SSID as your network in an attempt to capture unsuspecting users. Once connected to an attacker's AP, legitimate users will attempt to connect to your network's resources such as the email server and Web-based applications. Although they'll be unable to connect to these resources through the attacker's AP, they might be duped into revealing their usernames and passwords before throwing their hands up in frustration. You should train your Help desk staff to be on the lookout for calls about wireless network connectivity problems that might point to such APs and ensure that staffers ask users to report their location. Follow up on reports using NetStumbler or other tools and check the MAC address of all APs in the area to make sure that each is legitimate.
If you find you need more information about securing a wireless network, an excellent resource for businesses of all sizes, and even home users, is the book Deploying Secure 802.11 Wireless Networks with Microsoft Windows by Joseph Davies (Microsoft Press, 2003). You can find information about the book and where to purchase it and you can link to a white paper that updates the book at http://www.microsoft.com/mspress/books/6749.asp. A great online resource is http://www.microsoft.com/windowsserver2003/technologies/networking/wifi/default.mspx. Although this page is in the Windows 2003 section of the Microsoft Web site, it contains links to information for XP.
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