Internet Connection Sharing (ICS) allows multiple computers in a small office or home office to access an Internet connection using a single public IP address. For example, you may have a computer in an intranet that connects to the Internet by using a dial-up connection. By enabling ICS on the computer that uses the dial-up connection, you can provide Internet access to all computers in the network. ICS provides network address translation, address allocation, and name resolution services for all computers on your network. ICS can also be enabled for high-speed networks, such as Integrated Services Digital Network (ISDN), Digital Subscriber Line (DSL), and cable-based Internet connections.

Setting up the Host Computer - Windows 98 (Second Edition)

1. Before you start, the computer must be able to dial out and access the internet.
2. Installing the ICS Component - Now you're ready to install ICS. Note that if something is done incorrectly, you'll have to start this section over. That means removing the ICS component, restarting Windows, and then attempting to add it again.
• Double-click on the Add/Remove Programs icon in Control Panel, and choose the Windows Setup tab.
• Highlight the Internet Tools without altering the checkbox next to it. If you check or uncheck this box, click Cancel and try again.
• Click Details, and then put a checkmark next to the first item, Internet Connection Sharing. For now, don't add or remove any other components - it'll just make it more complicated. If the ICS option is already checked, you'll have to uncheck it now, click Ok, wait for the system to reboot, and then attempt to add it again.
• Click Ok, and then Ok again. There will be some delays, some hard disk access, and some more delays. Insert the Windows CD when prompted.
• The next thing you see should be the Internet Sharing Setup Wizard. Important: Don't click Cancel or restart your computer before completing this Wizard. There's no way to start it again, so if it's interrupted, you'll have to start over, which means removing and reinstalling ICS.
• Click Next at the first information screen.
3. A new adapter called Internet Connection Sharing has been added.
4. An instance of Internet Connection Sharing (protocol) should appear bound to your two network cards, and the Internet Connection Sharing adapter, like this:
   • Internet Connection Sharing (protocol) -> Your first ethernet card
   • Internet Connection Sharing (protocol) -> Your second ethernet card, or Dial-Up Adapter
   • Internet Connection Sharing (protocol) -> Internet Connection Sharing
   Any other instances of this protocol can be removed. For example, if you're using it with two network cards, you can remove the instance that points to your Dial-Up Adapter.
5. Next, you'll see three new instances of TCP/IP, like this:
   • TCP/IP (Home) -> Your first ethernet card
   • TCP/IP (Shared) -> Your second ethernet card, or Dial-Up Adapter
   • TCP/IP -> Internet Connection Sharing
   The (Home) instance refers to the device used to connect the host to the rest of the home network - if you select it and click Properties, you'll notice that an IP address (usually 192.168.0.1) has been asigned to it. The (Shared) instance refers to the device used to provide the shared Internet connection - it has no interesting properties. The last entry is what used to be the TCP/IP properties of your internet connection that you entered here.
6. In addition, each of the other protocols you had installed (e.g. NetBEUI) are now also bound to the new Internet Connection Sharing adapter.

Setting up the Host Computer - Windows 2000

1. Open Network and Dial-up Connections
2. Right-click the shared connection, and then click Properties.
3. On the Sharing tab, verify the Enable Internet connection sharing for this connection check box is selected, and then click Settings.
4. If you want to configure a network application for the computers sharing the connection, on the Applications tab, click Add, and then do the following:
   • In Name of application, type an easily recognized name for the application.
   • In Remote server port number, type the port number of the remote server where the application resides, and then click either TCP or UDP.
   • In TCP or UDP or both, type the port number for the port on your home network that the application will connect to. Some applications require TCP and UDP port numbers.
5. If you want to configure a service to provide to users on remote networks, on the Services tab, click Add, and then do the following:
   • In Name of Service, type an easily recognized name for the service.
   • In Service port number, type the port number of the computer where the service resides, and then click either TCP or UDP.
   • In Name or address of server computer on private network, type the name or TCP/IP address of the computer on your home network where the service resides.

Setting up the Host Computer - Windows XP

1. At this point, it's a good idea to make sure your current Internet connection is operational by testing it (load a web page or something). If all is well, then you can continue.

2. .Choose the Sharing tab, and turn on the Enable Internet Connection Sharing for this connection option.

3. There's nothing useful behind the Settings button, so just click Ok when you're done. That's it! (Most likely, Windows will not make you restart, although if you are prompted, do so now.)

Note

Do not enable ICS in an existing network that has DNS servers, gateways, DHCP servers, or computers configured with static IP addresses. If your Windows 2000 Professional – based computer is in a network where one or more of these conditions exist, you must use Windows 2000 Server network address translation.

ICS is a version of a network address translator (NAT). A network address translator is an IP router defined in RFC 1631 that can translate IP addresses and TCP/UDP port numbers of packets as they are being forwarded. Consider a small business network with multiple computers connecting to the Internet. A small business normally has to obtain an Internet Service Provider (ISP)–allocated public IP address for each computer on its network. With a NAT, however, the small business can use private addressing (as described in RFC 1918) and have the NAT map its private addresses to a single or to multiple public IP addresses as allocated by its ISP. ICS uses the private network 192.168.0.0 with a subnet mask of 255.255.255.0 for all computers in an ICS-enabled network, permitting a maximum of 254 hosts.