EAP

Published: April 30, 2010

Applies To: Windows Server 2008, Windows Server 2008 R2

With the Extensible Authentication Protocol (EAP), an arbitrary authentication mechanism authenticates a remote access connection. The exact authentication scheme to be used is negotiated by the remote access client and the authenticator (either the remote access server or the Remote Authentication Dial-In User Service [RADIUS] server). Routing and Remote Access includes support for EAP-TLS by default. You can plug in other EAP modules to the server running Routing and Remote Access to provide other EAP methods.

EAP allows for an open-ended conversation between the remote access client and the authenticator. The conversation consists of authenticator requests for authentication information and the responses from the remote access client. For example, when EAP is used with security token cards, the authenticator can separately query the remote access client for a name, PIN, and card token value. As each query is asked and answered, the remote access client passes through another level of authentication. When all questions have been answered satisfactorily, the remote access client is authenticated.

An EAP authentication scheme is known as an EAP type. Both the remote access client and the authenticator must support the same EAP type for successful authentication to occur.

EAP-TLS

EAP-Transport Level Security (EAP-TLS) is an EAP type that is used in certificate-based security environments. If you are using smart cards for remote access authentication, you must use the EAP-TLS authentication method. The EAP-TLS exchange of messages provides mutual authentication, negotiation of the encryption method, and encrypted key determination between the remote access client and the authenticator. EAP-TLS provides the strongest authentication and key determination method.

EAP-TLS is supported only on servers that are running Routing and Remote Access, that are configured to use Windows Authentication or RADIUS, and that are members of a domain. A remote access server running as a stand-alone server or a member of a workgroup does not support EAP-TLS.

EAP-RADIUS

EAP-RADIUS is not an EAP type, but the passing of EAP messages of any EAP type by an authenticator to a RADIUS server for authentication. For example, for a remote access server that is configured for RADIUS authentication, the EAP messages sent between the remote access client and remote access server are encapsulated and formatted as RADIUS messages between the remote access server and the RADIUS server.

EAP-RADIUS is used in environments where RADIUS is the authentication provider. An advantage of using EAP-RADIUS is that EAP types do not need to be installed at each remote access server, only at the RADIUS server. In the case of a server running Network Policy Server (NPS), you only need to install EAP types on the NPS server.

In a typical use of EAP-RADIUS, a server running Routing and Remote Access is configured to use EAP and to use an NPS server for authentication. When a connection is made, the remote access client negotiates the use of EAP with the remote access server. When the client sends an EAP message to the remote access server, the remote access server encapsulates the EAP message as a RADIUS message and sends it to its configured NPS server. The NPS server processes the EAP message and sends a RADIUS-encapsulated EAP message back to the remote access server. The remote access server then forwards the EAP message to the remote access client. In this configuration, the remote access server is only a pass-through device. All processing of EAP messages occurs at the remote access client and the NPS server.

Routing and Remote Access can be configured to authenticate locally, or to a RADIUS server. If Routing and Remote Access is configured to authenticate locally, all EAP methods will be authenticated locally. If Routing and Remote Access is configured to authenticate to a RADIUS server, all EAP messages will be forwarded to the RADIUS server with EAP-RADIUS.

Enabling EAP

To enable EAP-based authentication, you must do the following:

  1. Enable EAP as an authentication protocol on the remote access server.

  2. Enable EAP and, if required, configure the EAP type on the appropriate network policy.

  3. Enable and configure EAP on the remote access client.

Additional considerations

  • Make sure your network access server (NAS) supports EAP before you enable it on a network policy on an NPS server. For more information, see your NAS documentation.

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