How To Set Up Internet Connection Sharing in Windows Server 2003

For a Microsoft Windows 2000 version of this article, see
307311 .


Internet Connection Sharing (ICS) permits you to use Windows Server 2003 to connect a small office network or home network over the Internet. ICS provides Network Address Translation (NAT), IP addressing, and name resolution services for all the computers on a small network. This step-by-step article describes how to install ICS on a Windows Server 2003-based computer.

The following hardware or software is required for this procedure:
  • A digital subscriber line (DSL) or cable modem connected to an Internet service provider (ISP) and an activated DSL or cable account.
  • Two installed network adapters. This article describes how to install a second network adapter.
  • A network already configured with functioning TCP/IP.
CAUTION: Before proceeding with the procedures in this article, note the following points:
  • Do not use ICS on a network that:

    • Uses static IP addresses
    • Has a Windows Server 2003 domain controller
    • Uses other DNS servers, gateways, or DHCP servers

    Because ICS creates a static IP address for your network adapter and allocates IP addresses to other computers on your network, you will lose your connection to the rest of the network if other network computers already provide those services. If one or more of these conditions exist in your network, you must use Windows Server 2003 NAT instead of ICS. For more information about NAT, see Windows Server 2003 Help.
  • Do not create a virtual private network (VPN) connection to a corporate network from the ICS computer. If you do, by default all traffic from the ICS computer, including traffic from local area network clients, will be forwarded over the VPN connection to the corporate network. This means that Internet resources will no longer be reachable, and all the client computers will be sending data over the logical connection created with the credentials of the ICS computer user.
  • Do not configure ICS on a computer that is a VPN server. If your Windows Server 2003-based computer is serving as a VPN server, you must use Windows Server 2003 NAT.

How to Install a Second Ethernet Network Adapter to the ICS Host Computer

To install another Ethernet adapter to the ICS host computer, you must log on as a member of the Administrators group.
  1. Shut down your computer properly, and then physically add the network adapter.
  2. Restart your computer.
  3. When the Found New Hardware dialog box is displayed that lists the name of the network adapter that you installed, click Next.
  4. Click Next on the Install Hardware Device Drivers page.
  5. On the Locate Driver Files page, click the media option that contains the drivers for the network adapter that you are installing. For example, click CD-ROM drive, Floppy drive or Hard Drive Directory.
  6. On the Driver Files Search Results page, click Finish.

    NOTE: When you click Finish, the installation of the network adapter that you just installed is completed.

How to Configure the ICS Host Computer

The ICS host computer provides a connection through the second network adapter to the existing TCP/IP network. Log on as member of the Administrators group to set up the ICS host computer.
  1. Click Start, click Control Panel, and then click Network Connections.
  2. Right-click Local Area Connection (the network card that you just installed), and then rename it
    The Internet Connection.

    In the
    Network and Dial-up Connections dialog box, two connections are displayed (for different network adapters): The Internet Connection and Local Area Connection.
  3. Right-click The Internet Connection, and then click Properties.
  4. Click the General tab, and then verify that Client for Microsoft Networks and Internet Protocol (TCP/IP) are displayed.
  5. Click the Advanced tab, and then click to select the Enable Internet Connection Sharing for this Connection check box.

    NOTE: Make sure that firewall software or other Internet sharing software from any third-party manufacturer have been removed.
  6. Click OK, and then return to the desktop.

How to Configure the Windows Client

NOTE: Because there are several versions of Microsoft Windows, the following steps may be different on your computer. If they are, see your product documentation to complete these steps.

Log on as a member of the Administrators group to set up the Windows clients that will share the Internet connection.
  1. Click Start, click Control Panel, and then double-click Network Connections.
  2. Right-click Local Area Connection, and then click Properties.
  3. Click the General tab, and then verify that Client for Microsoft Networks and Internet Protocol (TCP/IP) are displayed and selected.
  4. Click Internet Protocol (TCP/IP), and then click Properties.
  5. Click the General tab, click Obtain an IP address automatically, and then click Obtain DNS server address automatically (if these options are not already selected).
  6. Click Advanced, and then make sure that the various lists on the IP Settings, DNS, and WINS tabs are all empty.

    Note that ICS provides these settings.
  7. Click OK, and then return to the desktop.

ICS and Dial-up Networking

You can use Dial-up Networking to connect to the Internet. However, Dial-up Networking typically has a lower bandwidth connection. This connection is not as useful when multiple computers share the connection. Additionally, Dial-up Networking is not persistent (you have to manually dial up to make a connection) and can cause initial delays when you connect to hosts on the Internet.


Note the following items to prevent issues from occurring when you configure ICS:
  • Do not connect a hub directly to your DSL or cable modem. If you do so, your internal network is vulnerable to other computers located on the Internet. If you do connect a computer directly to a DSL or cable modem, make sure that you turn off file and printer sharing to limit your vulnerability from the Internet. However, when you do so, your network is prevented from sharing files and printers, which may be your primary reason for networking in the first place.
  • Verify that firewall software or other Internet sharing software from third-party manufacturers has been removed. Make sure that only the ICS-enabled computer is providing IP addresses, forwarding DNS names, or acting as a default gateway. If not, ICS may not work or you may experience unexpected behavior.
  • You cannot modify the configuration of ICS. For example, you cannot prevent ICS from allocating IP addresses or modify the IP addresses that ICS has allocated. If these features are required, you must run NAT instead.
  • The ICS computer automatically assigns IP addresses, forwards DNS names to the Internet for name resolution, and assigns itself as the default gateway for connections to the Internet. If the ICS-enabled computer is unavailable, the other client computers on your network cannot access the Internet.
  • When you configure your network to use TCP/IP, remove instances of the NetBEUI protocol when you find them. NetBEUI is redundant and may slow down the network.