Callback Security Available Only from Microsoft Windows NT (137941)

SYMPTOMS

When you use Dial-Up Networking to dial into a Point-to-Point Protocol (PPP) or Remote Access (RAS) server, callback security may not work properly and the connection may fail.

CAUSE

The Windows Dial-Up Networking client supports the callback security feature only from a Microsoft Windows NT 3.x or 4.0 RAS server. Also, the default properties of the modem initialization string in the Windows client disable the modem's auto-answer feature.

RESOLUTION

The Dial-Up Networking client supports only the CallbackCP control protocol for processing server callback security services. Currently, Windows NT 3.x and Windows NT 4.0 support this protocol.

PPP and RAS servers for other platforms and operating systems would have to use the Microsoft CallbackCP protocol in order for the Dial-Up Networking client to access their callback security services.

To allow the Windows client to answer the callback verification from a Windows NT 3.x or 4.0 RAS server, follow these steps:

In Control Panel, double-click Modems.
Click the modem you are using, and then click Properties.
On the Connection tab, click Advanced.
In the Extra Settings box, type the following line:

AT S0=1

This string allows the modem to answer the callback from the Windows NT server.
Click OK or Close until you return to Control Panel.

MORE INFORMATION

Callback security can be used to audit the use of remote servers using either of the following methods:

The first method is for the remote user to dial into the server and enter a phone number for callback. After the remote user enters the callback number, the connection is dropped and Windows waits for the Windows NT server to call back to establish the remote session.
The second method is to have a server-side preset phone number. When the remote user calls in, the Windows NT server checks the user list for a phone number. At that point, the connection is dropped and the Windows NT server calls the preset number. The preset number can be changed only at the server side.