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IAS as a RADIUS proxy

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

IAS as a RADIUS proxy

Internet Authentication Service (IAS) can be used as a RADIUS proxy to provide the routing of RADIUS messages between RADIUS clients (access servers) and RADIUS servers that perform user authentication, authorization, and accounting for the connection attempt. When used as a RADIUS proxy, IAS is a central switching or routing point through which RADIUS access and accounting messages flow. IAS records information in an accounting log about the messages that are forwarded.

The following illustration shows IAS as a RADIUS proxy between RADIUS clients (access servers) and either RADIUS servers or another RADIUS proxy.

IAS as a RADIUS proxy

When IAS is used as a RADIUS proxy between a RADIUS client and a RADIUS server, RADIUS messages for network access connection attempts are forwarded in the following way:

  1. Access servers, such as dial-up network access servers, VPN servers, and wireless access points, receive connection requests from access clients.

  2. The access server, configured to use RADIUS as the authentication, authorization, and accounting protocol, creates an Access-Request message and sends it to the IAS server that is being used as the IAS RADIUS proxy.

  3. The IAS RADIUS proxy receives the Access-Request message and, based on the locally configured connection request policies, determines where to forward the Access-Request message.

  4. The IAS RADIUS proxy forwards the Access-Request message to the appropriate RADIUS server.

  5. The RADIUS server evaluates the Access-Request message.

  6. If required, the RADIUS server sends an Access-Challenge message to the IAS RADIUS proxy, where it is forwarded to the access server. The access server processes the challenge with the access client and sends an updated Access-Request to the IAS RADIUS proxy, where it is forwarded to the RADIUS server.

  7. The RADIUS server authenticates and authorizes the connection attempt.

  8. If the connection attempt is both authenticated and authorized, the RADIUS server sends an Access-Accept message to the IAS RADIUS proxy, where it is forwarded to the access server.

    If the connection attempt is either not authenticated or not authorized, the RADIUS server sends an Access-Reject message to the IAS RADIUS proxy, where it is forwarded to the access server.

  9. The access server completes the connection process with the access client and sends an Accounting-Request message to the IAS RADIUS proxy. The IAS RADIUS proxy logs the accounting data and forwards the message to the RADIUS server.

  10. The RADIUS server sends an Accounting-Response to the IAS RADIUS proxy, where it is forwarded to the access server.

You can use IAS as a RADIUS proxy when:

  • You are a service provider that offers outsourced dial, virtual private network (VPN), or wireless network access services to multiple customers. Your network access servers send connection requests to the IAS RADIUS proxy. Based on the realm portion of the user name in the connection request, the IAS RADIUS proxy forwards the connection request to a RADIUS server that is maintained by the customer and can authenticate and authorize the connection attempt. For more information, see Realm names.

  • You want to provide authentication and authorization for user accounts that are not members of either the domain in which the IAS server is a member or another domain that has a two-way trust with the domain in which the IAS server is a member. This includes accounts in untrusted domains, one-way trusted domains, and other forests. Instead of configuring your access servers to send their connection requests to an IAS RADIUS server, you can configure them to send their connection requests to an IAS RADIUS proxy. The IAS RADIUS proxy uses the realm name portion of the user name and forwards the request to an IAS server in the correct domain or forest. Connection attempts for user accounts in one domain or forest can be authenticated for network access servers in another domain or forest.

    IAS supports authentication across forests without a RADIUS proxy when the two forests contain only domains that consist of domain controllers running Microsoft® Windows Server® 2003, Standard Edition; Windows Server 2003, Enterprise Edition; and Windows Server 2003, Datacenter Edition. The forest functional level must be Windows Server 2003 , and there must be a two-way trust relationship between forests. If you use EAP-TLS with certificates as your authentication method, however, you must use a RADIUS proxy for authentication across forests that consist of Windows Server 2003 domains.

  • You want to perform authentication and authorization by using a database that is not a Windows account database. In this case, connection requests that match a specified realm name are forwarded to a RADIUS server, which has access to a different database of user accounts and authorization data. Examples of other user databases include Novell Directory Services (NDS) and Structured Query Language (SQL) databases.

  • You want to process a large number of connection requests. In this case, instead of configuring your RADIUS clients to attempt to balance their connection and accounting requests across multiple RADIUS servers, you can configure them to send their connection and accounting requests to an IAS RADIUS proxy. The IAS RADIUS proxy dynamically balances the load of connection and accounting requests across multiple RADIUS servers and increases the processing of large numbers of RADIUS clients and authentications per second.

  • You want to provide RADIUS authentication and authorization for outsourced service providers and minimize intranet firewall configuration. An intranet firewall is between your perimeter network (the network between your intranet and the Internet) and intranet. By placing an IAS server on your perimeter network, the firewall between your perimeter network and intranet must allow traffic to flow between the IAS server and multiple domain controllers. When replacing the IAS server with an IAS proxy, the firewall must allow only RADIUS traffic to flow between the IAS proxy and one or multiple IAS servers within your intranet.

For more information, see Deploying IAS as a RADIUS Proxy.

Note

  • You can configure IAS in Windows Server 2003, Standard Edition, with a maximum of 50 RADIUS clients and a maximum of 2 remote RADIUS server groups. You can define a RADIUS client using a fully qualified domain name or an IP address, but you cannot define groups of RADIUS clients by specifying an IP address range. If the fully qualified domain name of a RADIUS client resolves to multiple IP addresses, the IAS server uses the first IP address returned in the DNS query. With IAS in Windows Server 2003, Enterprise Edition, and Windows Server 2003, Datacenter Edition, you can configure an unlimited number of RADIUS clients and remote RADIUS server groups. In addition, you can configure RADIUS clients by specifying an IP address range.

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