Chapter 18

RAS and TCP/IP

Understanding RAS

RAS (Remote Access Service) enables multiple users to dial in to you network. The users can use the services of the RAS server or the services of the entire network. 

Before a user can use RAS, they must have dial-in permissions assigned to them (User Manager) and the RAS server must be installed

There are three types of callback security (Dial-In permissions)

• Preset To: user must be calling from this number to gain access, otherwise NT hangs up and calls back preset number.
• Set By Caller:  User dials into server, sets the number for system to call back. (used when you got folks that travel a lot)
• No Call Back:  is selected when you do not wish to configure callback security.

Installing RAS Server (p 512)

Setting Telephony API Properties (pp 518-519)

This is used when you've got staff that require access from multi locations because of travel.

Configuring RAS to Dial Out

You can select if you want RAS to be one of three methods:

• Dial Out Only: you can place outgoing calls
• Receive Calls Only: others can dial in
• Dial Out and Receive Calls: both options.

Select method the dial out protocols to be used, then you must select security method/options

• Allow any authentication including clear text:  this method is recommended by clients that do not support logon data encryption (broadest range of encryption options including clear text.
• Require encrypted  authentication:  wide variety of clients to connect using MS-CHAP, and other Challenge Handshake Authentication Protocol.
• Require Microsoft-encrypted authentication:  most secure authentications supported by RAS, requires client to support MS-CHAP. If this is selected and you check Require data encryption, all DATA transferred between clients and server are encrypted using the RSA Data Security Incorporated RC4 algorithm.

Dial-Up Networking

Dial-Up Networking is where you will keep the information about each of the locations you will dial into, found either in My Computer or the control panel.  Two types of protocol used in Dial-Up Networking are PPP (Point-to-Point Protocol) and SLIP (Serial Line Interface Protocol)

You need to configure at least one phonebook entry to use Dial-Up Networking. You can use the wizard to configure this.  (pp 522 - 524)

ISDN requires special metal wires and supports data transfer rates of 64 Kbps (64,000 bits per second). Most ISDN lines offered by telephone companies give you two lines at once, called B channels. You can use one line for voice and the other for data, or you can use both lines for data to give you data rates of 128 Kbps, three times the data rate provided by today's fastest modems.

Server Protocol Properties

PPP:

Short for Point-to-Point Protocol, a method of connecting a computer to the Internet. PPP is more stable than the older SLIP protocol and provides error checking features.

1. Multilink PPP and Dynamic Bandwidth Allocation

The 3ComImpact^(TM) External Digital Modem utilizes digital service available from the telephone company to transmit information. Generally, access to the Integrated Services Digital Network (ISDN) from the home is provided by a Basic Rate Interface (BRI). A BRI consists of two bearer (B channels) and one data (D channel). A B channel carries voice and data at a rate of 56 Kbps or 64 Kbps. The D channel carries network-related messages such as status and control information. By using Multilink PPP, the B channels can be combined to provide a maximum transmission speed of 128 Kbps, which is four times as fast as V.34 analog modems.

Multilink PPP is a protocol standard which provides higher access speeds and allows interoperability with Multilink PPP-compliant equipment from other vendors. Multilink PPP allows the two B channels to be used as a single transmission pipe. By combining the two B channels, a maximum transmission rate of 112 Kbps or 128 Kbps can be attained. With Multilink PPP, the two B channels are virtually linked, as shown in Figure 1. By default, Multilink PPP is enabled.

Dynamic Bandwidth Allocation

A feature of the 3ComImpact External Digital Modem, dynamic bandwidth allocation (DBA) automatically provides bandwidth when needed to place an outgoing voice call. (DBA does not apply to incoming voice calls.) When Multilink PPP is enabled, both B channels are dedicated to the data call. However, while Multilink PPP is active, you may want to place a voice call. With Dynamic Bandwidth Allocation (DBA), you can place a voice call while a Multilink PPP call is active.

Suppose, while connected to the Internet, you want to place a voice call using an analog phone attached to the 3ComImpact External Digital ModemOs phone port as shown in Figure 2. However, both B channels are being used by Multilink PPP for a data call.

With DBA, once you lift the telephone handset, one of the B channels used for Multilink PPP is temporarily and automatically removed and used to place the voice call. The temporary removal of a Multilink PPP link for a voice call reduces the speed of the data call in progress to 64 Kbps. The reliability of the data call is not affected. When the voice call ends (that is, when you replace the handset) the channel used for the voice call is once again reinstated for Multilink PPP.

SLIP

Short for Serial Line Internet Protocol, a method of connecting to the Internet. Another more common method is PPP (Point-to-Point Protocol). SLIP is an older and simpler protocol, but from a practical perspective, there's not much difference between connecting to the Internet via SLIP or PPP. In general, service providers offer only one protocol although some support both protocols.

PPTP

Short for Point-to-Point Tunneling Protocol, a new technology for creating Virtual Private Networks (VPNs) , developed jointly by Microsoft Corporation, U.S. Robotics, and several remote access vendor companies, known collectively as the PPTP Forum. A VPN is a private network of computers that uses the public Internet to connect some nodes. Because the Internet is essentially an open network, the Point-to-Point Tunneling Protocol (PPTP) is used to ensure that messages transmitted from one VPN node to another are secure. With PPTP, users can dial in to their corporate network via the Internet.

Dialing with a Phonebook Entry

Once you've created entries you want to dial, the next step is to use the entry, (see pp 531 - 532)

Dial-Up Networking Monitor

This utility enables you to perform many different functions and also provides you with information about the current connection. (pp536 - 539).

There are three tabs on Monitor settings.  Status, Summary, and Preferences

Summary tab determines which modem you must connect to which service, and can also be used to see if multilink session with a server has been correctly established.

Preferences tab enables you to customize the way the monitor works.

Using RAS as Internet Router

Once RAS is configured and has been tested, you can configure RAS as a router that enables other users on your network to access the Internet.

To Configure RAS as an Internet router, you need the following:

• A PPP connection (Dial-UP) to Internet (ISP)
• An Internet Class address or a valid IP subnet and subnet mask, assigned by Internet access provider
• A domain name and server if you want to have your local computers identified through DNS
• NT computer configured with a high-speed modem and serial card.