Configuring Internet Authentication Services (IAS)
Windows Server 2003 IAS is fully compatible with Windows 2000, so you can mix and match components as you upgrade your system.
If you have an existing third-party RADIUS implementation, you need to check the UDP ports used by the RRAS servers and the RADIUS servers. The current RADIUS standard uses UDP port 1812 for authentication and UDP port 1813 for accounting. Older RADIUS implementations used port 1645 for authentication and 1646 for accounting. If you have existing RADIUS servers or network access servers, they may use the old port number. You can configure IAS to use the old port number if the port conflict does not impact your current operations.
A server meeting the minimum memory and CPU requirements for Windows Server 2003 can handle tens of thousands of users. Ordinarily, you should install IAS on a domain controller. This eliminates any network delays in the transactions between the IAS service and Active Directory. This is not a requirement, however. IAS can process a large number of authentication requests per second regardless of whether it is running on a domain controller or as a standalone server. A Global Catalog (GC) server should be available in the same site as the IAS server.
When you've chosen the server to act as the IAS server, install the IAS service using the Add or Remove Programs applet in Control Panel. There is no need to restart. After the service is running, you can configure logging and remote access policies, register the server with Active Directory so it can perform authentication transactions, and configure it to accept RADIUS requests from the RRAS server.
Configuring IAS Logging and Remote Access Policies
Figure 20.44 shows the default configuration of the IAS management console, Ias.msc. This console is listed under ADMINISTRATIVE TOOLS in the START menu.
Figure 20.44. IAS management console.
The RADIUS Clients folder is used to configure relationships between the IAS server and RRAS servers. This is covered in the next section.
The Remote Access Logging folder contains the configuration interface for the RADIUS accounting feature. This takes the form of a Local File icon. The log file controlled by the accounting feature is stored under \Windows\System32\Logfiles. The configuration settings for the logging feature are exposed in the Properties window.
Ordinarily, you would want to select all logging options. This ensures that you have a record if someone abuses her dial-up privileges or if an exploit occurs. The IAS log file can grow fairly large. The Local File tab has an option for changing the file's location and for creating new logs periodically, such as every day or week or month depending on the number of users and the size of the logs.
When it comes to configuring remote access policies, you may be taken back a little by the large number of configuration possibilities in RADIUS. The standard was designed for ISPs that handle millions of users and need lots and lots of policies.
Under normal circumstances, you only need a policy that grants dial-in access to users. This policy is created by default and resides in the Remote Access Policies folder.
The default setting for this policy is to Deny Remote Access Permission. Change this to Grant when you are ready to permit dial-in connections. Before this policy takes effect, though, the user account in Active Directory must be configured to use remote access policies. This option is only available in Native.
Registering an IAS Server with Active Directory
An IAS server cannot use Active Directory to authenticate users until the IAS service has been "registered" in Active Directory. This registration consists of adding the computer account for the IAS server into the RAS and IAS Servers group.
You can add the IAS server to the RAS and IAS Servers group manually, but you may find it more convenient to use the server registration feature in the IAS console. This only adds the server into the RAS and IAS Servers group in its own domain. If you have IAS servers in several domains and users need to cross-authenticate, you must manually add the IAS servers to the RAS and IAS Servers groups in all domains. Use the steps in Procedure 20.17 to register an IAS server in Active Directory.
Procedure 20.17 Registering an IAS Server with Active Directory
Right-click the Internet Authentication Service icon and select REGISTER SERVICE IN ACTIVE DIRECTORY from the flyout menu.
A message appears notifying you that the computers that are running IAS must be authorized to read users' dial-in properties and prompting you to confirm that you want to do this. Click OK to confirm.
A notice appears informing you that the server has been registered. You are also reminded that it must be added to the RAS and IAS Servers group in any trusted domains to authenticate users from those domains.
At this point, the IAS server is ready to process authentications. Now, configure the RRAS server to be a client of the IAS server.
Configuring IAS and RRAS to Support RADIUS Authentication
Before an IAS server will accept RADIUS authentication requests from an RRAS server, there must be a trust relationship between servers. Like a classic NT trust, this trust has a secret password that the two machines share. This permits the IAS server to validate the identity of the RRAS server to prevent man-in-the-middle exploits. To configure an RRAS server as an IAS client, follow Procedure 20.18.
Procedure 20.18 Configuring an RRAS Server as an IAS Client
In the IAS console, right-click the Clients icon and select ADD CLIENT. The Add Client window opens.
Enter the name of the RRAS server in the Friendly Name field. (This is used only for display.) The only available protocol is RADIUS.
Click Next. The Client Information window opens. Under Client Address, enter the fully qualified DNS name or IP address of the RRAS server.
Under Client-Vendor, select Microsoft. This tells the IAS server to use a Windows domain controller for handling incoming RADIUS authentication requests.
Under Shared Secret, enter a password that the IAS and RRAS servers will share. This password is not changed dynamically, so make sure it is long and complex to prevent someone from setting up an RRAS server at the same IP address to spoof authentication requests.
Click Next to save the changes.
Now, configure the RRAS server to use RADIUS and point it at the IAS server by following Procedure 20.19.
Procedure 20.19 Configuring RRAS to Use RADIUS Authentication
In the Routing and Remote Access console, open the Properties window for the server icon.
Select the Security tab.
Under Authentication Provider and Accounting Provider, select the RADIUS options.
Next to the Authentication Provider field, click Configure to open the RADIUS Authentication window. This holds a list of the RADIUS servers that will be used by this RRAS server.
Click Add. The Add RADIUS Server window opens.
Under Server Name, enter the fully qualified DNS name or IP address of the IAS server.
Next to the Secret field, click Change to open the Change Secret window.
Enter the password you entered in the client configuration at the IAS server and click OK.
Click OK to add the IAS server to the list of RADIUS servers. The Initial Score column shows the default score of 30. The RRAS server will change this score based on how quickly it gets responses back from the RADIUS servers. There is seldom a need to set this value manually.
Perform the same actions for the Accounting Provider.
Stop and start the RRAS service to initialize the new providers.
At this point, the RRAS server is ready to accept client connections. You can test the configuration by making a standard dial-in connection using a domain account. The RRAS server will authenticate using the domain credentials supplied by the IAS server.