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11. Remote Access Service (RAS)




RAS and Dial-Up networking use SLIP (Unix servers) or PPP. NT Workstation can have only one RAS connection whereas Server can have up to 256. Modems, ISDN or X.25 can be used. NT detects modems automatically, although you can configure them manually from the Modems program. NT can connect to an X.25 network using a smart card that contains a PAD or an asynch connection to a PAD via a COM port.

Point to Point Tunnelling Protocol has been developed by Microsoft to allow users to gain secure access to Virtual Private Networks over the Internet. The connection to the Internet is first required before a RAS connection can be established to the RAS server connected to the Internet. The IP encapsulated packets are PPP packets that can contain IP, NetBEUI or IPX. The client requires a PPTP driver for direct connection to the Internet unless the client has a connection via an ISP that supports PPTP.

SLIP only supports TCP/IP and requires a static IP address so DHCP and WINS cannot be used. It requires scripting for login and passwords are sent as clear text. NT does not have a SLIP server.

PSTN and ISDN lines can be combined with PPP Multilink. NT 3.1 used RAS but only supported NetBEUI.

The NT computer can act as a IP/IPX router using SAP and a NetBIOS gateway. The RAS server can allow users to access just the computer or the entire network using the RAS Server NetBEUI Configuration. The NetBEUI gateway translates NetBEUI packets to IP or IPX.

The same user accounts used on the LAN are used by RAS, the user must have a RAS password. Using auditing on User Manager for Domains you can find out who is dialling.

The default authentication is encrypted and an Intermediary Security Host can be added between the Dial-up Networking client and the RAS server. In addition, call back can be enabled to call a trusted site number. If a RAS server has a direct connection to the Internet, enabling PPTP filtering disables all protocols except PPTP on the network card. This is done in Advanced IP Addressing in the TCP/IP properties box.

The Telephone API (TAPI) allows you to centrally configure a computer for local dialling parameters. TAPI Service Providers (TSP) are drivers that control hardware such as a PBX.

Running the Telephony program allows you to access the Dialling Properties box which you use to configure a dialling location with area code, special code to dial out, country location, phone system etc.

Installation of RAS occurs through the Dial-up Networking icon in My Computer. The modem needs to be configured and then in Remote Access Service within the Networking program servics tab, add a port to make available for RAS and then configure the RAS settings for the port (COM1, COM2 etc.). The port can be set for Dial out only, Receive Calls Only or Dial out and Receive Calls.

Use the protocols tab to set the dial out protocols and encryption (PAP, CHAP and MS-CHAP). Multilink requires similar hardware to work i.e. NOT one modem and one ISDN TA.

A RAS server can allow TCP/IP clients to access the entire network or just that computer. It can also decide whether to use DHCP to assign an IP address or use a Static Address Pool for the RAS server to assign the IP address or the client can use a predetermined IP address. The same options are available for IPX addresses.

When the client's Dial-Up Networking is configured you can decide the interval and number of dial attempts, the appearance and the phone book to be used. Using the User Profiles tab in System allows you to use the locally-cached user profile instead of a server-based profile just in case the server is down when a user dials in to log on.

In TCP/IP and NetBEUI autodialling is allowed whereby the network address is mapped to the phonebook entry.

If a Security log fills up then it stops you logging on and you need to use the Admin log on to correct it. Event Viewer keeps a log that will eventually fill up the hard disk and overwrite itself. You can reduce this.

RAS problems are entered into the System log so use event Viewer to look at this. PPP problems can be can be examined by way of the PPP.log file which is activated by setting to 1 the following parameter HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services|Rasman\PPP\Logging.

The Dial-Up Monitor program in Control Panel allows you to show the status of the session in progress.

Multilink capability is lost during callback because only one number is allowed for dial back.


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