Installing Internet Connection Sharing

Internet Connection Sharing ( ICS ) was introduced in Windows 98 and is included as a feature of Windows 2000. ICS allows multiple computers on a local area network to simultaneously access the Internet using a single Internet connection. This technology provides home offices and small businesses with Internet connectivity without added cost because only one Internet connection is necessary for the entire LAN. ICS can be enabled on a Windows 2000 Professional workstation or Windows 2000 Server.

To connect multiple computers on a local area network to the Internet, at least one computer must have an Internet connection and have ICS enabled. Enabling ICS is as simple as checking a single box (this is basically the extent of configuring ICS). Once ICS is enabled, the following services are provided:

• Network Address Translation This component is responsible for mapping the private IP address of internal clients to a single public IP address.

• DHCP Allocator Provides a simplified version of the DHCP service. The DHCP Allocator assigns internal clients IP addresses in the range of 192.168.0.0/24 . The range assigned to clients is not configurable.

• DNS Proxy This component resolves DNS names to IP addresses for clients. It passes name resolution requests to the Internet-based DNS server configured in the TCP/IP properties of the external interface of the ICS computer.

• Auto-dial An ICS connection point can automatically dial when a client on the LAN attempts to access the Internet.

Before you enable ICS on a computer, keep the following points in mind:

• ICS should not be enabled on a network with other Windows 2000 domain controllers, DNS servers, DHCP servers, gateways, or other computers using static IP addresses. ICS assigns internal clients addresses from a non-configurable range that could interfere or conflict with the existing address scheme.

• Once ICS is enabled, the IP address of the internal interface is changed to 192.168.0.1 .

• Computers on the internal network must be configured to automatically obtain an IP address. The DHCP Allocator service assigns the clients an IP address.

• For ICS to function with an ISDN or modem, on-demand dialing must be enabled.

ICS should be used only when the computer with the shared connection is the only gateway on the network and no other server on the network is providing IP addressing to clients.

Enabling ICS

To enable ICS on a Windows 2000 computer, perform the following steps:

1. Click Start, point to Settings, and click Control Panel.

2. Double-click the Network and Dial-up Connections applet.

3. Right-click the connection for which you want to enable ICS and select Properties.

4. Select the Sharing tab from the Properties window.

5. Click the option to Enable Internet Connection Sharing for this connection (see Figure 8.1).

   Figure 8.1. Enabling Internet Connection Sharing from the Network and Dial-up Connections applet.

   

6. Select the box beside Enable On-Demand Dialing to have the computer auto-dial a connection when an internal client attempts to access the Internet.

Configuring ICS

After an administrator has enabled ICS, clients on the network can use their Web browsers and email applications as though they have their own direct Internet connection.

You might need to further configure ICS for applications and services to function; for example, when internal clients want to use the shared connection to play Internet-based games or hold videoconferences using NetMeeting. These types of services and applications require an incoming connection with an internal workstation. Also, if you are hosting Web services on the internal network, ICS must be configured to provide Internet users with access to the service.

Applications and services can be configured for ICS using the Settings button located on the Sharing properties sheet. Click the Settings button to display the Internet Connection Sharing Settings window (see Figure 8.2).

Figure 8.2. To configure ICS settings, you must add applications to be supported.

From the Applications tab, you can configure which applications are available to users on the internal network sharing the Internet connection. By default, no applications are listed. Click the Add button to configure an application and provide the following information (see Figure 8.3):

• Name of application Type a descriptive name for the application.

• Remote server port number Type the port number of the remote server where the application resides. Select TCP or UDP.

• Incoming response ports Type the TCP or UDP (or both) ports that the application connects to on the ICS computer.

Figure 8.3. Configuring applications available through ICS.

The Services tab lists all the services available for ICS (see Figure 8.4). To provide users on a remote network with access to a specific service, simply check the box beside the service. The window that appears allows you to specify the name or IP address of the computer on the network hosting the service.

Figure 8.4. Configuring services for ICS.

If you require additional services, click the Add button and provide the following information (see Figure 8.5):

• Name of service Type a descriptive name for the service.

• Service port number Specify the port number of the computer on which the service resides. Select UDP or TCP.

• Name or address of server computer on private network Type the name or IP address of the computer on the internal network hosting the service.

Figure 8.5. Configuring additional services for ICS.

Configuring ICS Clients

Configuring a client to use a shared Internet connection is a relatively straightforward process. You simply configure the TCP/IP properties for the local area connection to automatically obtain an IP address. Also, using the Connection tab from the Properties window for Internet Explorer, make sure that the Never Dial a Connection option is selected and the following options on the Local Area Connection Settings window (see Figure 8.6) are deselected:

• Automatically detect settings

• Use automatic configuration script

• Use a proxy server

Figure 8.6. Configuring the properties of Internet Explorer on an ICS client.