This article discusses Remote Authentication Dial-In User Service (RADIUS) authentication in Microsoft Internet Security and Acceleration (ISA) Server 2006 and ISA Server 2004.

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RADIUS authentication is useful when ISA Server is installed in workgroup mode. RADIUS servers do not require domain membership of RADIUS clients. The ISA Server computer acts as a RADIUS client from which authentication requests originate. ISA Server passes information about a user to a designated RADIUS server and then acts on the response that the RADIUS server returns. Transactions between the ISA Server computer and the RADIUS server are authenticated by a shared secret. The shared secret is never sent over the network.

RADIUS servers authenticate the following requests:

•	Incoming remote client virtual private network (VPN) requests to ISA Server
•	Outgoing requests from internal clients
•	Requests from external clients in publishing scenarios

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For more information about how to use RADIUS authentication for ISA Server 2006, visit the following Microsoft Web site:

For more information about how to use RADIUS authentication for ISA Server 2004 VPN remote client connections, visit the following Microsoft Web site:

For more information about Outlook Web Access server publishing in ISA Server 2004 by using RADIUS and Forms-based client authentication, visit the following Microsoft Web site:

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