Troubleshooting Internet Connection Sharing in Windows XP (308006)

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When you use Connection Sharing, you can share one Internet connection between two or more computers. Before you install or use Connection Sharing, you should contact your Internet service provider (ISP) or read your ISP's Terms and Conditions of Use policy to determine if you are permitted to share your connection.

Host configuration

To install Connection Sharing, you can either use the Network Setup Wizard or configure the shared connection manually.

To run the Network Setup Wizard, follow these steps:

1. Click Start, point to All Programs, point to Accessories, point to Communications, and then click Network Setup Wizard.
2. Click Next until you see the Select a connection method dialog box.
3. Click This computer connects directly to the Internet, and then complete the wizard to successfully install Connection Sharing.

For additional information about configuring Connection Sharing manually, click the following article number to view the article in the Microsoft Knowledge Base: Using the Network Setup Wizard to configure Connection Sharing has the following advantages:

• It automatically tries to detect the connection to the Internet.
• It can configure Internet Connection Firewall (ICF).
• It can bridge multiple network adapters that are connected to your home network.
• It logs information about the configuration that was performed by the wizard in the %SystemRoot%\Nsw.log file.

If the Connection Sharing installation not successful, check the following:

• Verify that Internet connectivity is functional from the Connection Sharing host computer before sharing the connection.
• Make sure that the interface to be shared is compatible with ICS. One-way connections, such as a satellite connection that uses both a satellite interface for downloading data and a dial-up connection for uploading data, are not compatible with Connection Sharing in Windows XP.
• Make sure that your have selected the correct interface as the shared connection. The shared interface must be the one that is connecting to the Internet.
• If you are trying to configure Connection Sharing manually for a connection, make sure that the home network adapter does not have ICF enabled. If ICF is enabled, you must either disable it before you can configure Connection Sharing on the external connection or use the Network Setup Wizard to enable ICS. The wizard disables ICF on home networking interfaces.
• Verify the IP address on the shared connection to confirm that it is obtaining an IP address from your ISP.
• Verify the IP address on the internal adapter to confirm that it is assigned as 192.168.0.1. If it is not, disable Connection Sharing on the shared connection, make sure that the internal adapter is configured to obtain an IP address automatically, and then enable ICS on the shared adapter.
• Check the system log and the Nsw.log file for errors that are related to ICS configuration. To view the contents of Nsw.log, click Start, click Run, type nsw.log, and then click OK.

When the installation issue has been resolved and Connection Sharing is enabled, verify that Internet connectivity is still functional on the ICS host computer before you test the ICS client computers.

Note: Install Connection Sharing only on the computer that you use to connect to the Internet. This computer is referred to as the "host" computer. The other computers on the local area network (LAN) that use the host to connect to the Internet are referred to as "client" computers. If you configure Connection Sharing on multiple computers on your network, you may receive error messages that indicate that computers have duplicate IP addresses.

Client configuration and connectivity

After you verify connectivity on the host computer and verify that it can browse correctly in Microsoft Internet Explorer, troubleshoot the configuration and connectivity on the client computers. Follow these steps:

1. Open Internet Explorer to test the opening of a Web page. If Internet Explorer does not open successfully, continue with the following steps. Make sure that you test Internet Explorer after each step to determine whether the issue is resolved.
2. Check the IP address that is assigned to the client by going to the Network Connections folder and double-clicking the adapter that is connected to the home network. This will open the status interface. On the Support tab, make sure that the assigned IP address is in the range 192.168.0.x (where x is a number between 2 and 254). If it is not, troubleshoot physical connectivity between the host computer and the client computer, and verify that the client computer is configured to receive an address by way of Dynamic Host Configuration Protocol (DHCP). To check the DHCP settings, follow these steps:
   1. Open the properties of the adapter on the client computer.
   2. Click to select Internet Protocol (TCP/IP) in the list of clients and protocols, and then click Properties.
   3. In the TCP/IP Properties dialog box, on the General tab, verify that the Obtain an IP address automatically and the Obtain DNS server address automatically check boxes are selected.
   4. If you still do not have a valid IP address assigned after checking these settings, try setting the TCP/IP properties manually. Set the IP address for an unused IP address, 192.168.0.x, where x is a number between 2 and 254 that is not already in use on the home network. Set the subnet mask for 255.255.255.0, the default gateway for 192.168.0.1, and the preferred and alternate DNS server settings for 192.168.0.1.
3. Ping the Connection Sharing host address 192.168.0.1 to test connectivity to the host computer. To do this, follow these steps:
   1. Click Start, click Run, type the cmd command, and then click OK.
   2. Type the following command to ping the host computer:

      ping 192.168.0.1

      You will see a series of replies, such as the following, that indicate that connectivity to the host computer is working:

         Reply from 192.168.0.1: bytes=32 time<1ms TTL=128

   If this is not successful, there may be a connectivity issue, or you may have a problem with TCP/IP on the client computer. To rule this out, ping the IP address of the client computer. If this is successful, but the ping to the host address was not successful, there is likely a physical connectivity issue between the two computers.
4. Use Internet Explorer to open a Web page by using the IP address. You can obtain the IP address of a Web site on the Internet by using the ping command from the Connection Sharing host computer. Verify that the host computer receives a correct reply from the Web server, because some servers do not respond to ping requests.
   
   If you cannot open pages in Internet Explorer by using the IP address, but the previous steps were successful, try to open a local .html file. If you can, there is likely a connectivity or Winsock issue on the client computer. Troubleshoot this behavior as if Connection Sharing were not in the configuration. For additional information about viewing the contents of the system log, click the following article number to view the article in the Microsoft Knowledge Base:

   308427 How to view and manage event logs in Event Viewer in Windows XP

5. If you can open the Web site by using the IP address, try opening pages by using the fully qualified domain name (FQDN), such as http://www.microsoft.com. Failures at this point indicate that there is a name resolution issue. Verify that the client computer is configured to use 192.168.0.1 as its DNS server. You can check this by clicking Details on the Support tab of the adapter status. If 192.168.0.1 is not displayed as the DNS server, follow these steps:
   1. Open the properties of the adapter on the client computer.
   2. Click Internet Protocol (TCP/IP) in the list of clients and protocols, and then click Properties.
   3. Verify on the General tab of the TCP/IP Properties dialog box that the Obtain DNS server address automatically check box is selected.
   After you check this, verify that 192.168.0.1 is now displayed as the DNS SERVER address for the client computer, and then retest connectivity.