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Components of a RADIUS infrastructure

Updated: January 21, 2005

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

Components of a RADIUS infrastructure

A RADIUS authentication, authorization, and accounting infrastructure consists of the following components:

  • Access clients

  • Access servers (RADIUS clients)

  • RADIUS proxies

  • RADIUS servers

  • User account databases

These components are shown in the following illustration.

A dial-up example

Access clients

An access client is a device that requires some level of access to a larger network. Examples of access clients are dial-up or virtual private network (VPN) clients, wireless clients, or LAN clients connected to a switch.

Access servers (RADIUS clients)

An access server is a device that provides some level of access to a larger network. An access server using a RADIUS infrastructure is also a RADIUS client, sending connection requests and accounting messages to a RADIUS server. Examples of access servers are:

  • Network access servers (NASs) that provide remote access connectivity to an organization network or the Internet. An example is a Windows 2000 computer running the Routing and Remote Access service and providing either traditional dial-up or virtual private network (VPN) remote access services to an organization's intranet.

  • Wireless access points that provide physical layer access to an organization's network, using wireless-based transmission and reception technologies.

  • Switches that provide physical layer access to an organization's network, using traditional LAN technologies such as Ethernet.

RADIUS proxies

A RADIUS proxy is a device that forwards or routes RADIUS connection requests and accounting messages between RADIUS clients (and RADIUS proxies) and RADIUS servers (or RADIUS proxies). The RADIUS proxy uses information within the RADIUS message, such as the User-Name or Called-Station-ID RADIUS attributes, to route the RADIUS message to the appropriate RADIUS server.

A RADIUS proxy can be used as a forwarding point for RADIUS messages when the authentication, authorization, and accounting must occur at multiple RADIUS servers in different organizations.

RADIUS servers

A RADIUS server is a device that receives and processes connection requests or accounting messages sent by RADIUS clients or RADIUS proxies. In the case of connection requests, the RADIUS server processes the list of RADIUS attributes in the connection request. Based on a set of rules and the information in the user account database, the RADIUS server either authenticates and authorizes the connection and sends back an Access-Accept message or sends back an Access-Reject message. The Access-Accept message can contain connection restrictions that are implemented by the access server for the duration of the connection.

User account databases

The user account database is the list of user accounts and their properties that can be checked by a RADIUS server to verify authentication credentials and user account properties containing authorization and connection parameter information.

The user account databases that IAS can use are the local Security Accounts Manager (SAM), a Microsoft Windows NT 4.0 domain, or the Active Directory directory service. For Active Directory, IAS can provide authentication and authorization for user or computer accounts in the domain in which the IAS server is a member, two-way trusted domains, and trusted forests with domain controllers running Windows Server 2003, Standard Edition; Windows Server 2003, Enterprise Edition; and Windows Server 2003, Datacenter Edition.

If the user accounts for authentication reside in a different type of database, IAS can be configured as a RADIUS proxy to forward the authentication request to a RADIUS server that does have access to the user account database. Different databases for Active Directory include untrusted forests, untrusted domains, or one-way trusted domains.


  • 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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