Dell PowerConnect W Clearpass 100 Software 3.9 Deployment Guide - Page 131

When using this option, the guest's username and password credentials will be sent to a value provided in the URL. As this is a potential security hazard, enter the known IP addresses of the controllers in your network in the Allowed Dynamic and Denied Dynamic fields, to prevent an information leak vulnerability that could be exploited by guest users on your network. The second section requires you to specify the behavior of the Web login form. There may only be some fields displayed here, depending on which of the Vendor Settings you have chosen. The Authentication field provides three options:  Credentials-a username and password. The guest is prompted for a username and password to log in to the network.  Access Code-Requires only username for authentication. The guest's password is automatically provided for the login attempt.  Anonymous-This option supports two special usernames: _mac and underscore (_). When Anonymous is selected, two usernames may be used to enable specific behavior. The guest is not prompted for a username and password; a fixed set of credentials will be used for all guest logins. If you select this option, then the Auto-generate (optional) and Anonymous User (required) fields display.  _mac: This populates the username and password with the user's MAC if the user is detected on the system. To enable this first navigate to Administrator > Plugin Manager > MAC Authentication Plugin. Select the Configuration icon to display the MAC Authentication Plugin page. Select the Allow users to be detected via their MAC address option and click Save Configuration. On the RADIUS Web Login page, select Anonymous in the Authentication field. Check the Autogenerate the anonymous account option. Make sure to select the Pre-Auth Check option Local - match a local account and save the configuration.  Underscore (_): Leaves the username and password blank and requires post-processing in the header or footer. Pre-authentication checks now take place:  None - No checks will be made: No checks are made before redirecting to the NAS login.  Local -Match local account: Checks the entered username and password before redirecting to the NAS login.  RADIUS - Check using RADIUS request: Checks the local database and external authenticationservers for the provided credentials. This provides authentication of the user regardless of where the account is defined. ClearPass Guest 3.9 | Deployment Guide RADIUS Services | 131