Dial-Up Networking for Windows NT and Windows 95 Clients

In Microsoft Windows NT version 4.0, the Remote Access Service (RAS) client has been renamed to Dial-Up Networking (often referred to as DUN) and has been given a new look to be consistent with Microsoft Windows 95. This enhancement enables users to connect via DUN in Windows 95 or Windows NT 4.0, without having to learn and understand different interfaces.

DUN allows you to connect to any dial-up server using the Point-to-Point protocol (PPP) as a transport mechanism allowing for TCP/IP, NetBEUI or IPX/SPX network access over your analog modem, ISDN, or X.25 Pad devices. Windows NT can also be configured as a SLIP client connecting to a third-party SLIP server. By default, DUN setup is initiated after you install a modem on your computer. During configuration you will be prompted to create a phonebook entry that you can then use to store your connection settings for future use.

Windows NT version 4.0 has also added a check box so that you can log on via DUN when you enter your Ctrl+Alt+Del key sequence. When you check this box, the program displays the DUN phonebook where you can select an entry to dial, in order to log on. DUN then establishes a connection to the RAS server, to reach a domain controller for the specified domain to validate your logon request.

Support of LAN and WAN Protocols

As an integrated service within Windows NT, RAS supports the TCP/IP, IPX/SPX and NetBEUI protocols. When you configure a RAS server in Windows NT to allow network traffic from your dial-up clients, you can enable use of one or all of these protocols.

Support for Connections across PSTN, ISDN, X.25 and the Internet

The Remote Access Service allows for connections across several media. The most common of these is the Public Switched Telephone Network (PSTN). PSTN is the technical name for the medium you use every day to make phone calls and send faxes. Hardware requirements for RAS over PSTN are any combination of analog modems supported on the Windows NT Hardware Compatibility List (HCL) placed at the originating and receiving ends of an asynchronous connection. Most RAS connectivity you will be supporting in your networks will be over PSTN. Almost every new laptop or desktop computer nowadays comes pre-configured with a modem—just as every home, office, and hotel is equipped with a phone line.

ISDN (Integrated Services Digital Networks) connections take place over digital lines and provide faster and more reliable connectivity. ISDN has been a very successful and popular choice in some areas, but it has not caught on at all in others. The primary benefit of ISDN is its speed and reliability. ISDN is commonly found in two speeds:64kbps and 128kbps. Connection speed is determined by how many ‘B’ channels your telephone company or Internet Service Provider (ISP) is willing to give you and/or how much you are willing to pay. A ‘B channel’ allocates 64kb of bandwidth and the lesser-known ‘D channel’ allocates a small amount of bandwidth for error-correction and transmission verification. Often you will hear someone refer to his or her ISDN implementation as 2B+D which would indicate a 128kbps ISDN connection. However, ISDN hasn’t caught on everywhere, primarily due to its cost and limited availability.

X.25 networks transmit data with a packet-switching protocol, bypassing noisy telephone lines. Clients can access an X.25 network directly by configuring DUN to use an X.25 PAD (packet assembler/disassembler). For more information on X.25, see your Windows NT documentation, the Windows NT Resource Kit, and Microsoft TechNet.

New to Windows NT 4.0 is the ability to utilize the new PPTP in your organization. Now, instead of having your organization absorb the costs of creating, managing, and maintaining a large RAS server or servers, including all of the necessary modems and other hardware, you can implement PPTP. PPTP provides a secure method to outsource the hardware and support portion of remote network access to Internet Service Providers (ISP). With the implementation of PPTP, a company needs only to set up a RAS server with Internet access and manage user accounts and permissions. The company can then use a dedicated service provider, such as a telephone company or local ISP, to manage the dial-in lines, modems, ISDN cards, and so on. For example, a user would dial a modem pool maintained by their local service provider. Once connected to the Internet, the user would then establish a second DUN session, requesting the TCP/IP address of your RAS server across the Internet This connection will provide them with the equivalent remote network access you would have had by directly calling the RAS server— all at greatly reduced hardware and support cost. PPTP is also an excellent solution for minimizing long distance charges and eliminating the need for an 1-800 number.

Using Multi-Modem Adapters with NT Server (Multilink)

RAS Multilink combines two or more physical links, most commonly analog modems, into a logical "bundle." This bundle acts as a single connection to increase the available bandwidth/speed of your link. Multilink requires that you have multiple WAN adapters installed on both the client and the serving computer and that both are configured to use Multilink. For example, if ISDN were not available in your area and you required more bandwidth than a typical 28.8 modem could provide, you could combine four 28.8kbps modems on your workstation and four modems on the receiving RAS server for a whopping combined bandwidth of 115.2kbps bundled aggregate. It's a reasonable solution indeed, considering the next option is an expensive and sometimes unavailable 128kbps 2B+D ISDN link. Now imagine being able to Multilink multiple ISDN lines. You can! Remote Access Service performs PPP Multilink dialing over multiple ISDN and modem lines.

If a client is using a Multilinked phonebook entry to dial to a server that is enforcing callback (discussed later under RAS Security), only one of the Multi-linked devices will be called back. Only one callback number can be stored in a user's RAS permissions, allowing only one device to connect. All other devices will fail to complete the connection, and the client loses Multilink functionality. Multilink is callback-compatible only if the Multi-linked phonebook entry uses both channels for ISDN and both channels are using the same phone number.

Q & A

Remote Access Protocols

RAS connections to your network are established over the Serial Line Internet Protocol (SLIP) or the Point-to-Point Protocol (PPP). PPP is an improvement over the original SLIP specification and is the primary choice for most Microsoft RAS implementations. PPP is fully supported by the Remote Access Service in both a server and client role. SLIP is only supported under Windows NT as a dial-up client to a third party or UNIX SLIP server.

Serial Line Internet Protocol (SLIP)

The Serial Line Internet Protocol (SLIP) was developed to provide TCP/IP connections over low-speed serial lines. Plagued by limitations such as lack of support for WINS and DHCP, Microsoft has chosen PPP for their Remote Access standard. However, Microsoft has also provided SLIP support for Windows NT dial-up networking, giving clients access to TCP/IP and Internet services through a SLIP server. Often, SLIP connections rely on text-based logon sessions and require additional scripting by a host or Internet Service Provider (ISP) to automate the logon process. This, combined with a lack of support for NetBEUI and IPX/SPX, has been the primary reason for the popularity of PPP and the decrease in SLIP connectivity in Microsoft networks.

Point-to-Point Protocol (PPP)

PPP enables DUN clients and RAS servers to interoperate in complex networks. PPP supports sending TCP/IP, NetBEUI, IPX/SPX, AppleTalk and DECnet data packets over a point-to-point link. The Microsoft RAS implementation of PPP supports the standard Windows NT protocols: TCP/IP, NetBEUI and IPX/SPX.

Windows NT Protocols over PPP

RAS and TCP/IP

With the booming popularity of the Internet, the Transmission Control Protocol/Internet Protocol (TCP/IP) is commonly found in most new and existing networks. On a TCP/IP network, unique TCP/IP addresses are given to every host. This also applies to all hosts connecting through RAS. Typically, any computer connecting to a RAS server via PPP on a Microsoft TCP/IP network is automatically provided an IP address from a static address pool provided by the RAS server or allocated dynamically from a DHCP server. A RAS administrator may also choose to permit users to request a specific address by entering a valid IP address in their DUN configurations.

As in any TCP/IP LAN, most users do not want to have to remember all sorts of complicated IP addresses. Name resolution for IP addresses helps ease network naming in a TCP/IP environment. All name resolution methods available on a Windows NT network are also available to clients connecting through RAS. A RAS server can take advantage of the Windows Internet Name Service (WINS), broadcast name resolution, the Domain Name System (DNS), HOSTS and LMHOSTS files. DUN clients are assigned the same WINS and DNS servers that are assigned to the RAS server unless you modify the registry to override them. DUN clients are also able to select their own WINS and DNS servers by specifying them in their DUN settings. If WINS or DNS is not available on your network, DUN clients can use HOSTS or LMHOSTS files configured locally for name resolution.

RAS and NetBEUI

NetBEUI is a small and fast network protocol commonly found in small, local area networks with 1 to 200 users. Like TCP/IP and IPX/SPX, NetBEUI is supported by RAS allowing NetBEUI packets access through your RAS server to your network. Once installed, the only additional configuration NetBEUI requires is making the decision to allow remote users to access your entire network or just the RAS server the user is connecting to. The RAS server NetBEUI Configuration screen is illustrated in Figure 11-1.

RAS and IPX

IPX is the protocol introduced by Novell and implemented in most Netware environments. Like TCP/IP, it is a routable protocol—making it very popular for large enterprise-wide networks. A Windows NT RAS server behaves as an IPX router and Service Advertising Protocol (SAP) agent for DUN clients. Once RAS is configured with IPX, file and print services, as well as the use of Windows Sockets applications, are available to DUN clients.

When a DUN client connects to an IPX network through a RAS server, an IPX network number is provided to the client by RAS and SAP services are provided by the RAS server. The IPX network number can be automatically generated by the RAS server using the Netware Router Information Protocol (RIP). Manual IPX network number assignments can also be configured within RAS. However, when assigning an IPX network number to a RAS server, be sure not to select any numbers already in use on your network. A single network number can be assigned to all DUN clients on your RAS server to minimize RIP announcements.

RAS PPTP

Windows NT 4.0 iintroduces direct remote access support to the Internet with the implementation of the Point-to-Point Tunneling Protocol (PPTP). Using PPTP, a user can establish a connection to the Internet through a local ISP (Internet Service Provider). Once connected to the Internet, the user initiates a connection to your network by requesting the IP address of the RAS server. This is referred to as Virtual Private Networking (VPN). PPTP offers the following advantages over other WAN solutions:

Installing the PPTP on your server is a three-step process. First, establish connectivity to the Internet with your RAS server. Next, install the PPTP as you would any other protocol in Windows NT and indicate the number of Virtual Private Networks you want to implement. Finally, apply any PPTP filtering you require to the TCP/IP protocol by choosing the Advanced button in the TCP/IP protocol settings. Enabling PPTP filtering will effectively remove all other protocol support on that adapter, securing your network from intruders.

Once PPTP is installed on the server, you will be able to establish a connection to it over the Internet with a PPTP enabled client, such as Windows NT Workstation. To initiate a VPN, a user will first need to use DUN to dial an ISP and establish an Internet connection. The user would then use DUN again to ‘Dial’ the RAS server using the IP address of your RAS server as the phone number and the Virtual Private Network number as the port.

Q & A

Installing and Configuring Remote Access Service

A RAS server can be installed during the installation of Windows NT or at any other time by adding it as a network service. Prior to installing RAS, you should be aware of the following:

Before installing RAS you may also want to consider installing your modems first. If your modems are working prior to the installation of RAS, you can eliminate most hardware issues when troubleshooting RAS connectivity problems.

Exercise 11-1: Installing a RAS device

1. To install a modem in Windows NT, double-click the Modems icon in the Control Panel.
1. If a modem is already present on your system, the Modems Properties screen will open. If no modems are currently installed, the Install New Modem wizard, shown in Figure 11-2 will open.

3. Choose Next to have Windows NT attempt to detect your modem.
4. If Windows NT finds your modem, you can choose Finish to complete the setup of your modem. If a modem was not detected, you can then choose to install a modem from the list of Windows NT supported modems. You can also choose to load drivers for your modem from disk (Illustrated in Figure 11-3).

3. Once you have selected a modem click Next. You then have the opportunity to choose what port you want to install the modem on.
4. Click Finish to exit the modem installation screen. You will be returned to the Modem Properties screen (shown in Figure 11-4) where you can add another modem or modify your current selections.

If your modem is not listed in the supported modems list, you can modify the MODEM.INF file and create your own modem type. Simply add the name of your modem in brackets followed by any modem initialization strings that your particular modem requires. These commands are commonly found in your modem's documentation.

Exercise 11-2: Installing the RAS

1. To install RAS, double-click the Network icon in the Control Panel. This will open the Network Settings screen.
1. Select the Service tab and press the Add button.
1. In the Select Network Service screen, choose Remote Access Service and click OK.
1. The program will request the location of your Windows NT Server or Workstation setup files. Insert your Windows NT CD-ROM and supply the information needed to access it. Click OK.
1. After the files required for RAS have been copied to your system, the RAS setup program will prompt you for the first device you want RAS to initialize. If you don’t already have a RAS-capable device (such as a modem) installed, you can select the Install Modem or Install X.25 Pad buttons to configure new devices. When you select the Install Modem button, the Install New Modem wizard will walk you through the modem hardware installation.
1. Once RAS setup has a valid device configured for use with RAS, you may configure each RAS port as shown in Figure 11-5, adding support for the network protocols you require.

After you have successfully installed RAS, you will need to restart your system for the changes to take effect.

Exercise 11-3: Removing/Uninstalling RAS

1. If you later decide to change the role of your server or workstation and want to remove RAS from the system, double-click the Network icon in Control Panel to open the network Configuration screen.
1. Select the Services tab, select Remote Access Service from the list of installed services and click the Remove button. Choose Yes to accept the warning that RAS will be permanently removed from your system.
1. Click Close. When prompted to restart your computer, click Yes.

Removing the Remote Access Service will not remove any modems you may have installed. You can remove modems by selecting the Modems icon in Control Panel, selecting a modem and pressing the Remove button. If you remove a modem from your system, you will be prompted to reconfigure DUN.

Configuring RAS Ports

After you have installed a modem, ISDN device or X.25 PAD, you can configure the RAS port for each device. To configure a port, open RAS setup, choose a port and press the Configure button. You can also install a new modem directly from this dialog box by selecting the Add button. Once the ports have been configured for RAS you can then identify which role each port will play. Ports can be configured for dialing out, receiving calls, or both, as shown in Figure 11-6. If you set the port to receive calls, you may specify whether to give callers access to the entire network or restrict access to the RAS server only.

Exercise 11-4: Configuring port usage

1. In the Port Usage Configuration screen (Figure 11-6), specify how the port is to be used. Options are: dial out only, receive calls only, or both.
1. Click OK when you are finished. Calls cannot be received on a port until RAS has been started.

Exercise 11-5: Configuring an ISDN adapter

1. To configure or install a new ISDN adapter, choose the Network icon in Control Panel or right-click the Network Neighborhood icon on your desktop and choose Properties.
1. Choose the Adapters tab and click Add to install a new adapter or click Properties to modify your current adapter.
1. Configure your new ISDN port for dial out only, receive calls only or dial out and receive calls.

Configuring RAS Network Settings

When configuring RAS network settings such as protocol usage or encryption settings, keep in mind that any configuration settings you make will apply to all RAS operations for all RAS-enabled ports (see Figure 11-7). For example, if you were to enable NetBEUI support for Dial-Out settings on your server, all RAS capable devices on that server will support NetBEUI. The Remote Access Service, when installed on a RAS computer, can access a LAN as a server and as a client. For each role, you must configure how you want each port to be utilized. When configuring Dial-Out protocols, keep in mind that any protocols you do not enable in RAS Network Configuration will be unavailable to you when you later configure a phone book entry for dialing out. When setting up RAS to service remote clients, you must configure each protocol carefully so that RAS protocol settings don’t conflict with communications on the rest of your network. When choosing an encryption method, always apply the highest level of encryption possible, keeping in mind the encryption capabilities of your clients.

Exercise 11-6: Configuring a RAS server with TCP/IP

1. When configuring a RAS server to use TCP/IP for network connections, open the Control Panel and double-click the Network icon to start the network setup program.
1. On the Services tab, select the Remote Access Service and click the Properties button.
1. In the Remote Access Setup dialog box, click the Network button.
1. In the Server Settings box, make sure the TCP/IP check box is selected (if TCP/IP is installed) and then click Configure. See Figure 11-8 for an illustration of the RAS Server TCP/IP Configuration screen.



Figure 8: The RAS server TCP/IP Configuration screen

5. In the RAS Server TCP/IP Configuration dialog box, select whether to allow TCP/IP clients to access the entire network or the RAS server only.
1. If a DHCP server is available on your network, select ‘Use DHCP to assign remote TCP/IP addresses.’ This service dynamically assigns valid TCP/IP addresses to your dial-up clients.
1. If a DHCP server is not available, select Use static address pool. To configure a pool of valid and available addresses for your network, enter the beginning and ending range of TCP/IP addresses that you wish to allocate to your dial-up clients. You must assign at least two addresses. If you assign a large range of addresses, you can reserve some addresses from this list by adding them to the excluded ranges list.
1. If you prefer to have users specify a TCP/IP address in their DUN configuration, select the Allow remote workstations to request a predetermined IP address check box.
1. Click OK.
1. In the Network Configuration dialog box, click OK.
1. In the Remote Access Setup dialog box, complete any additional port configurations and then click Continue. You must restart your server for these changes to take effect.

Exercise 11-7: Configuring a RAS server with IPX/SPX

1. To configure a RAS server to use IPX for network connections, open Control Panel and double-click the Network icon.
1. The network setup screen will appear. On the Services tab, select the Remote Access Service and then click the Properties button.
1. In the Remote Access Setup dialog box, click the Network button.
1. In the Server Settings box, make sure the IPX check box is selected (if IPX is installed) and then click Configure. (See Figure 11-9 for an illustration of the RAS Server IPX Configuration screen).



Figure 9: The RAS Server IPX Configuration screen

5. In the RAS Server IPX Configuration screen, select whether to allow IPX clients to access the entire network or the RAS server only.
1. Choose ‘Allocate network numbers automatically’ if you want to allow RAS to use the Router Information Protocol (RIP) to determine an IPX network number that is not in use on your IPX network. If you want more control over IPX network number assignments, choose ‘Allocate network numbers’ and type your first network number in the From box. RAS will automatically determine the number of available ports and insert the ending network number for you.
1. Select ‘Assign same network number to all IPX clients’ if you want to assign the same network number to all connected IPX clients.
1. Select the ‘Allow remote clients to request IPX node number’ check box to allow the remote client to request its own IPX node number in their DUN configuration rather than use the RAS server-supplied node number.
1. Click OK.
1. In the Network Configuration dialog box, click OK. You must restart your server for these changes to take effect.