Isnin, 12 November 2007

The wireless local area network (WLAN) solution described in this documentation works equally well with either dynamic Wired Equivalent Privacy (WEP) or Wi-Fi Protected Access (WPA) WLAN protection. The implementation differences between the two are minor and are documented in this appendix.

Currently, there are some potential difficulties with using WPA, which include:

Manual configuration of WPA settings: The support for setting Windows XP client WPA settings using group policy is not available in the versions of Windows earlier than Windows Server™ 2003 Service Pack 1. Until Service Pack 1 is available and you have deployed it in your organization, you will have to configure your clients manually (there is no way to script WLAN settings for Windows XP). You need to install Service Pack 1 only on the server on which you are editing the WLAN settings Group Policy object (GPO); it is not required on the clients, domain controllers, or IAS servers.

Restricted availability of WLAN clients: At the time of writing, Microsoft only provides WPA support for Windows XP Service Pack 1 and later.

Availability of WPA compliant hardware: Although WPA support is now mandatory for all Wi-Fi certified hardware, existing network equipment may need to be upgraded to support WPA. You will need to obtain firmware updates for any access points or network adapters that do not currently support WPA. In some (rare) cases, you may need to replace equipment if the manufacturer does not produce WPA updates.

Using WPA in Place of WEP
Although the majority of the guide is applicable to both WPA and dynamic WEP, there are two main points in the documentation where the instructions differ:

• The “Creating an IAS Remote Access Policy for WLAN” section in Chapter 5, “Building the Wireless LAN Security Infrastructure.”

• The “Creating the WLAN Settings GPO” section in Chapter 6, “Configuring the Wireless LAN Clients.”

Creating an IAS Remote Access Policy for WLAN with WPA
To use WPA WLAN protection in place of dynamic WEP, you should set the client session time–out value to 8 hours instead of 60 minutes. WPA has an in–built mechanism to generate new WLAN encryption keys, so it does not need to force the clients to re–authenticate frequently. Eight hours is a reasonable value to ensure that clients have valid up–to–date credentials (for example, it ensures that a client cannot remain connected for excessive periods after its account has been disabled). In very high security environments, you can reduce this time–out value, if needed.

In the "Modifying the WLAN Access Policy Profile Settings" section in Chapter 5, “Building the Wireless LAN Security Infrastructure,” use the following procedure to set the remote access policy profile settings:

To modify wireless access policy profile settings:

1. In the Internet Authentication Service MMC, open the properties of the Allow Wireless LAN Access policy, and then click Edit Profile.

2. On the Dial-in Contraints tab, in the Minutes clients can be connected (Session-Timeout) field, type the value 480 (480 minutes or 8hours).

3. On the Advanced tab, add the Ignore-User-Dialin-Properties attribute, set it to True, and then add the Termination-Action attribute and set it to RADIUS Request.

You also need to change the session time–out in the wireless access point (AP) to match (or exceed) the time–out value set in this procedure.

Manually Configuring Windows XP WLAN Settings for WPA
Until GPO support becomes available in Windows Server 2003 Service Pack 1, you must configure WPA settings on the client manually. WPA is supported on Windows XP Service Pack 1 with the WPA client download installed (or on Windows XP Service Pack 2).

Note: When GPO support becomes available, you can also use the following procedure to create a Wireless Network Policy using the same settings.

To manually configure WPA WLAN settings:

1. Open the properties of the Wireless Network interface. If the WLAN is displayed in the Available Networks list, select it, and click Configure..., otherwise click Add (in the Preferred Networks section).

2. Type the WLAN name into the Network Name (SSID) field (if it is not already displayed there) and, in the Description field, enter a description of the network.

Note: If you have an existing WLAN and you intend to run this side–by–side with the 802.1X–based WLAN of this solution, you must use a different Service Set Identifier (SSID) for the new WLAN. This new SSID should then be used here.

3. In the Wireless Network Key section, select WPA (not WPA PSK) as the Network Authentication type and TKIP as the Data Encryption type. (If your hardware supports it, you can choose the higher strength Advanced Encryption Standard (AES) in place of TKIP).

4. Click the IEEE 802.1x tab, and select Protected EAP (PEAP) from the EAP Type drop–down list.

5. Click the Settings... button to modify the PEAP settings. From the Trusted Root Certificate Authorities list, select the root CA certificate for the CA. (This is the CA that you installed to issue IAS server certificates—see Chapter 4 for more details).

Important: If you ever need to re–install your CA from scratch (not just restore from backup), you will need to edit the client settings and select the root CA certificate for the new CA.

6. Ensure that Secured Password (EAP-MS-CHAP v2) is selected in the Select Authentication Method and check the Enable Fast Reconnect option.

7. Close each properties window by clicking OK.

Configuring Pocket PC 2003 for WPA
WPA was not supported natively in Pocket PC 2003 at the time of writing; however, this may be implemented in the future. Support for WPA on Pocket PC may also be available from other vendors.

Migrating from WEP to WPA
If you have deployed a secure WLAN solution based on dynamic WEP and want to migrate to WPA, you need to follow the steps in this section. You must ensure that you have deployed WPA software support (for example, the Windows XP WPA component) and hardware support (AP firmware and network adapter driver updates) prior to the migration. References in this procedure to configuring WPA settings in GPOs are only valid when the GPO is edited from Windows Server 2003 Service Pack 1 or later. This service pack had not been released at the time of writing. If you are not using Windows Server 2003 Service Pack 1 or later, follow the instructions given in the “Manually Configuring Windows XP WLAN Settings” section in this appendix.

To migrate from WEP to WPA, if your APs support dynamic WEP and WPA simultaneously:

1. Configure all wireless APs to support both dynamic WEP and WPA.

2. Create a new WLAN client settings GPO. Create a Wireless Network policy that configures the correct settings for WPA (refer to the procedure provided in the "Manually Configuring Windows XP WLAN Settings" section in this appendix). Then disable the existing WEP GPO and enable the WPA GPO so that all WPA settings are sent out to all clients. The clients will start using WPA on the WLAN following the next GPO refresh.

Note: If you are configuring your clients manually, you must disable the GPO that contains the WEP settings; if you do not do this, the manual WPA settings will be overwritten by the GPO.

3. Finally, you should update the IAS remote access policy session time–out and the client session time–out in the AP (as described in the "IAS Remote Access Policy" section earlier in this appendix).

To migrate from WEP to WPA, if your APs do not support simultaneous use of WEP and WPA:

1. Create a new WLAN SSID for the WPA network.

2. Edit the client network settings GPO and add the new SSID using WPA parameters (as described in the "Manually Configuring Windows XP WLAN Settings" section earlier in this appendix). If you are configuring your clients manually, you should configure them with the new SSID and WPA settings for that SSID. Do not remove the settings for the old WEP SSID in either case.

3. Working site–by–site, reconfigure your APs from WEP to WPA support, changing the SSID of the AP. As you reconfigure each AP, the clients will switch to the new SSID and use WPA.

4. Once you have reconfigured all APs, you can update the remote access policies on all IAS servers. You need to increase the session time–out value in the remote access policy (from 60 minutes to 8 hours) and change the same setting in the wireless APs (as described in the "IAS Remote Access Policy" section in this appendix).

5. Once the migration is complete, you can remove the WEP SSID from the GPO.

This section provides references to important supplementary information or other background material relevant to this appendix.

• The Cable Guy — March 2003, Wi-Fi Protected Access™ (WPA) Overview, available at the following URL:

• Microsoft Knowledge Base Article 815485, "Overview of the WPA Wireless Security Update in Windows XP," available at the following URL:

• Microsoft Press Pass Announcement on WPA Availability, available at the following URL:

• "Wireless 802.11 Security with Windows XP" white paper available at the following URL: