Learn Windows XP in 15 Minutes a Week, Internet Connection Sharing

by Jason Zandri

Windows XP Professional offers Internet Connection Sharing, which enables any computer to function similar to a proxy server. This installment of our series explores the basics of installing and configuring the feature.

Welcome to the 27th installment of "Learn Windows XP Professional in 15 Minutes a Week." This article will look at Internet Connection Sharing in Windows XP Professional.

[NOTES FROM THE FIELD] -- For the 70-270 exam, it is important the test taker understand Internet Connection Sharing in depth.

The Windows XP Professional operating system offers Internet Connection Sharing (ICS) as an added feature of the base operating system. Internet Connection Sharing is found on nearly all flavors of Windows: Windows XP Home Edition; Windows 98; Windows Millennium Edition; Windows 2000 Professional, Server, and Advanced Server; and Windows Server 2003, Standard Edition and Enterprise Edition.

With ICS, an administrator can configure a single system to connect to the Internet while other systems connect to the connecting host system for access -- much the same way that a Microsoft Proxy Server or Internet Security and Acceleration (ISA) Server enables clients to connect to the Internet.

[NOTES FROM THE FIELD] -- Windows XP Professional (as well as Windows 2000 Professional and NT4 Workstation) is limited to 10 simultaneous inbound connections for all transports and resource sharing protocols, combined. The maximum inbound limit for Windows XP Home Edition is five.

Additional information for Windows XP can be found at http://support.microsoft.com/?scid=kb;en-us;314882. For Windows 2000, the URL is http://support.microsoft.com/default.aspx?scid=kb;EN-US;122920.

The host system can connect to the Internet by any means: modem dial up, ISDN, ADSL, SDSL, as well as satellite or cable broadband.

[NOTES FROM THE FIELD] -- With regard to all of these different services, the total available bandwidth will be shared. For example, typical home use of ADSL allows for 384 Kbps upstream and a maximum downstream of 1.5 Mbps. Where a single system is concerned, it would have this bandwidth available to it. Two separate and single systems connected to independent phone lines would have a total of 384 Kbps upstream and 1.5 Mbps downstream speeds at any time, even if both systems were constantly and simultaneously transmitting and receiving data.

If one system is connected to the ADSL connection and can use ICS, and the second system connects through the host system, the two systems share a single 384 Kbps upstream speed and 1.5 Mbps downstream speed. If both systems are constantly and simultaneously transmitting and receiving data, the most either system can use is one-half the total available bandwidth. If a third system is added, all three get one-third the total bandwidth. And so on.

If other connected systems go idle, the remaining systems then procure the remaining available bandwidth for their own use while it is available.

The DNS Proxy functionality in ICS allows connected client systems to resolve DNS names by permitting the ICS host to perform the requested look up as well as any necessary forwarding for LAN clients.

The DHCP Allocator service of ICS is a simplified DHCP service that assigns the IP address, gateway, and DNS name server information on the local network to the corresponding clients as needed. This allows the systems on the LAN to obtain an IP address from the ICS host system and connect to the Internet via the host system using Network Address Translation (NAT).

NAT is used under ICS to map and track the internal private-source IP addresses the host system has sent to LAN clients that correspond to public-destination IP addresses. This allows Client1 and Client2 to call www.zandri.net via Host1 and have the Web browsers on Client1 and Client2 render the corresponding Web page. As far as the Web server at zandri.net is concerned, Host1 called for the index page twice; the Host system via NAT knows that it was doing this on behalf of Client1 and Client2 and has forwarded HTTP GET requests to the proper client systems.

When ICS is enabled on an available adapter it will be given a new static IP address to configure the client systems on the network so they can obtain an IP address automatically and the ICS' DHCP Allocator can assign an IP address.

[NOTES FROM THE FIELD] -- To set up ICS Discovery and Control on Windows 98, Windows 98 Second Edition, and Windows Millennium Edition systems, run the Network Setup Wizard from the installation CD (under most circumstances) and ensure Internet Explorer version 5.0 or later is installed.

Starting from the Control Panel, configuring ICS on the host system requires the following steps:

[NOTES FROM THE FIELD] -- The example that follows uses the Classic view of the Control Panel. Most Windows XP systems use the Category View by default. With the exception of the initial steps, everything performed on the Property pages is the same regardless of the initial view.

First, the locally logged-on administrator must highlight and right-click on the connection to enable ICS and call up the properties page. (In this demo, these steps will be performed on a Prodigy dial-up connection.)

In the ICS section of the properties page in the Advanced tab, select the "Allow other network users to connect through this computer's Internet connection" checkbox.

Drop the spinner box and choose (there may be more than one) the available network segment and client systems you wish to allow to connect to the system.

This example features three local area connection networks and one wireless network up for selection.

[NOTES FROM THE FIELD] -- If Internet Connection Firewall is enabled on any of these adapters, corresponding networks will not show up as available to use within this spinner box.

However, once Internet Connection Firewall is enabled for the Wireless Network Connection it is no longer present.

Client systems must also be enabled to create a demand dial connection by checking the "Establish a dial-up connection whenever a computer on my network attempts to access the Internet" checkbox.

[NOTES FROM THE FIELD] -- If this setting is enabled and the host system is not connected to the Internet, any client system that attempts to access the Internet (e.g., call a Web page) will not be able to and will receive an error like the one shown below. In general, this is not because the Web site itself is unavailable but rather because the Web site is unavailable to the client system, as the client system currently does not have access to the Internet.

Some admins may decide to allow end users on the network the direct ability to control or disable the shared Internet connection directly (other than allowing demand dial-up when an Internet connection is attempted). To do this, select the last checkbox available on the page.

[NOTES FROM THE FIELD] -- In most cases, this setting will be enabled to allow a client system to disconnect a Host session. Other connected client systems will likely not appreciate it.

To successfully configure the browsers on the client systems to use the ICS host system, open Internet Explorer on the client system and go to the Tools menu. Click Internet Options, and go to the Connections tab. Select the Never Dial a Connection radio button.

Then click the LAN Settings button in the LAN settings section of the Connections tab to bring up the extended settings property page.

Select the "Automatically detect settings" checkbox (you may need to also select the Use Automatic Configuration script checkbox if this is being used on the LAN; it is not a requirement) in the Automatic Configuration section.

The "Use a proxy server for your LAN" checkbox in the Proxy Server section must be left unchecked.

That wraps up this installment of "Learn Windows XP Professional in 15 Minutes a Week." As always, if you have any questions, comments, or even constructive criticism, feel free to drop me a note. I want to write solid technical articles that appeal to a wide range of readers and skill levels, and it is only through your feedback that I can be sure I am doing that.

Until next time, best of luck in your studies and remember:

"Any computer system connected to any network is subject to potential compromise."

This article was originally published on Saturday Feb 7th 2004
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