RAS Protocols

Few articles in this magazine generate as much feedback as those about Windows NT's Remote Access Service (RAS). In May, I gave an overview of how to install and configure RAS in "Remote Access Service." In this article, I address configuring protocols in RAS. I will look at the remote access protocols and the LAN protocols RAS supports.

Which Protocols Does RAS Support?
RAS supports two sets of protocols: remote access protocols and LAN protocols. When you use the Remote Access Service, NT uses the remote access protocols to make the RAS connection to another computer, the Internet, or an Internet Service Provider (ISP). These protocols include Point-to-Point Protocol (PPP), Serial Line Internet Protocol (SLIP), the Microsoft RAS protocol, and Point-to-Point Tunneling Protocol (PPTP). The LAN protocols that NT uses to communicate over the RAS connection can be any of the protocols that you use in NT, including NetBEUI, NWLink, or TCP/IP. I will look first at the remote access connection protocols and then at how you must configure the LAN protocols to work with RAS.

The Remote Access Protocols: Client Configuration
When you configure NT 4.0 RAS for a server, the software supports PPP connections. So, this configuration gives you options about which remote access protocol to employ on the client side only.

SLIP. NT's RAS supports SLIP, but only from the client side. RAS clients can connect to existing SLIP servers, but an NT RAS server will not act as a SLIP server. SLIP does not support authentication as part of the protocol, so logon sessions use clear-text transmission of usernames and passwords. Also SLIP cannot negotiate automatic network connection settings. The main use for the SLIP protocol is for connecting to mostly UNIX-based Internet servers.

To configure the RAS client (known as Dial-Up Networking--DUN--in Windows 95 and NT 4.0) for SLIP, open the Phonebook entry, click More, choose Edit entry and modem properties, select the Server tab, and select SLIP:Internet under the Dial-up server type box, as Screen 1, page 222, shows. Many SLIP servers require a logon exchange, so you have two options. Under the Script tab, you can select the Pop up a terminal window option. Or you can use a Switch.inf file to automate the exchange of logon parameters. See the references at the end of this article for information about the contents of the Switch.inf file.

PPP. PPP is the most commonly used remote access protocol. It's a great improvement over SLIP, offering automated, encrypted authentication (although some service providers that use PPP still require a text-based logon exchange). Clients and servers that use the PPP protocol will automatically negotiate authentication and network settings.

To configure PPP in the Phonebook entry, follow the steps outlined for SLIP, but select PPP: Windows NT, Windows 95 Plus, Internet as the Dial-up server type. As with the SLIP logon, if the remote server requires that you log on, set the script option to Pop up a terminal window so that you can interact with the server and provide the required information, or use a script file.

Microsoft RAS Protocol. In Windows NT 3.1 and Windows for Workgroups 3.11, Microsoft supplied an earlier version of the RAS client (at that time, Dial-Up Networking was called the RAS client). It supports both the RAS Terminal and Switch.inf script files for making logon connections.

PPTP. PPTP lets a remote user use a dial-up networking connection to connect to an ISP. This connection transmits data in secure, encapsulated form via the Internet to the corporate Remote Access Server. Essentially, you're using the Internet as a Virtual Private Network (VPN), which helps to reduce costs and maintain security. (For more about PPTP and RAS, see Sean Daily, "Watch Your RAS," August 1997.)

The LAN Protocols: Client Configuration
After you establish the connection between the RAS client and the RAS server, you must decide which LAN protocol to use over that connection. At the client end, you choose the protocol from the Server tab under the Edit Entry and Modem Properties dialog box, as we saw in Screen 1. For TCP/IP, you will need to configure some options.

NetBEUI and IPX/SPX on the client. You have no options to configure for NetBEUI on the client. The same applies to the IPX/SPX Compatible option.

TCP/IP on the client. TCP/IP requires considerably more configuration than any other protocol, as Screen 2 shows. First, determine whether your network has a Dynamic Host Configuration Protocol (DHCP) server that can supply an IP address. If not, you must enter a static IP address. This entry can result in problems unless you use the dial-up connection to connect to the same server each time. Most ISPs and most companies that have RAS servers use DHCP. Even with DHCP, you must decide whether the DHCP server will supply the name server addresses for the Domain Name System (DNS) and Windows Internet Name Service (WINS). This issue is less of a concern when you're connecting to a corporate server, which often will supply these addresses. ISPs, however, might require entries for the DNS server.