Outbound authentication using PPTP filtering

75 HKEY_LOCAL_MACHINE\SYSTEM\Services\RASPPTPE\Parameters\Configuration Add a new Registry entry with the data type REG_DWORD. Call the entry AllowPacketsForLocalMachine and give it a value of 1, then enter the changes and close the Registry Editor. Youll have to reboot for the change to take effect. As weve said before, however, we dont recommend that you run services that can cause security breaches anonymous FTP or disrupt the workings of your internal network DHCP on your RAS server.

5.1.4 Filtering by IP Address

Another type of security allows you to specify the IP addresses from which the RAS server will allow PPTP connections. In order to implement this, your remote users will need to have fixed IP addresses assigned by their ISPs, and youll need to know these addresses. Used in combination with PPTP filtering, this can make the RAS server secure from both unauthenticated connections and connections from unauthorized hosts. Unfortunately, this cant be done simply from a graphical user interface, so you must go back into the Windows NT 4.0 Registry. Run the Registry Editor again and go to the following Registry key: HKEY_LOCAL_MACHINE\SYSTEM\Services\RASPPTPE\Parameters\Configuration Under this key, youll need to create a new entry of data type REG_DWORD. The new entry should be called AuthenticateIncomingCalls. Make it a decimal value and give it a value of 1. Under the same key, create a new entry of data type REG_MULTI_SZ. Give this entry the name of PeerClientIPAddresses. This is where youll want to enter the valid IP addresses of the hosts you wish to be able to connect to the RAS server using PPTP. They should all be separated by single blank spaces.

5.1.5 Configuring Users for Dial-up Access

A dial-up user under Windows NT RAS is essentially set up the same way as a regular Windows NT domain user: 1. Use the User Manager for Domains, found under the Administrative Tools menu, to add or modify the user. 2. When editing the User Properties, click the Dialin button on the lower left- hand side of the dialog box. 3. The Dialin Information dialog box will appear see Figure 5-4 . For a PPTP user, check Grant dialin permission to user, and set the Call Back radio button to No Call Back.