Lesson 5: Troubleshooting Internet Connection Sharing

Internet Connection Sharing (ICS) offers a simple way to configure computers in a small home office network to share a single Internet connection. For small networks, ICS offers a cost-effective way to provide Internet access to multiple computers.

After this lesson, you will be able to

• Configure Internet Connection Sharing.

• Identify the limitations of ICS.

• Enable ICS on a computer running Windows XP.

Estimated lesson time: 10 minutes

Configuring Internet Connection Sharing

When you set up ICS on a network, the computer with the physical connection to the Internet (whether that be a modem, cable, or other type of connection) is designated as the ICS computer. Other computers on the network connect to the Internet through the ICS. In addition to providing Internet access, the ICS host computer also dynamically allocates IP addresses to the clients on the network, provides name resolution, and serves as the gateway for the other computers.

Setting up ICS on a small network consists of the following general steps:

1. Make sure that the computer that will become the ICS computer is properly connected to the Internet.

2. Make sure that the ICS computer and the other computers are properly connected to one another by means of a local network.

3. On the ICS computer, enable Internet Connection Sharing on the Internet network connection. This is done by selecting the Allow Other Network Users To Connect Through This Computer’s Internet Connection option on the Advanced tab of the network connection’s Properties dialog box. When you enable ICS, the ICS computer configures itself with the IP address 192.168.0.1 and also becomes a DHCP server for the network so that it can provide IP addressing information to other computers.

4. Configure the remaining computers to obtain their IP address and DNS server information automatically, and restart the computers. When each computer restarts, it will obtain addressing information from the ICS computer and should be able to connect to the Internet. IP addresses of the computers will fall in the range 192.168.0.2 through 192.168.0.254.

ICS Limitations

Because of what ICS does for a network (IP address allocation, name resolution, and acting as the network’s gateway), and because the IP address the host computer uses is always 192.168.0.1 with a subnet mask of 255.255.255.0, several conditions must be met while ICS is used:

• The IP addresses of the computers on the network must also be in the 192.168.x.y range, and the subnet mask must always be 255.255.255.0. If network computers cannot use these addresses, ICS will not work properly.

• Microsoft Windows 2000 Server or Windows Server 2003 servers configured as domain controllers, DNS servers, gateways, and DHCP servers cannot be used on the network.

• Computers with static IP addresses that do not fall in the ICS range will not work with ICS.

• If more than one network adapter is available, and if two or more local area connections are configured and all of them connect to computers on the network, those connections will need to be bridged. Bridging a connection is as simple as right-clicking the connection and selecting Bridge Connections.

• ICS must be enabled from the dial-up, virtual private network (VPN), broadband, or other connection to the Internet.

• You should not use this feature in a network with other domain controllers, DNS servers, gateways, or DHCP servers.

Problems can also occur with ICS if the host computer originally had a static IP address on the network or if the address 192.168.0.1 is being used by another computer on the network. (You can use ipconfig to find out.)

Note

If you are having a problem with an ICS configuration, check the items in the preceding bulleted list. Make the appropriate changes to the network to resolve the problem.

Troubleshooting ICS

Although you can troubleshoot ICS by using many of the connectivity troubleshooting methods already covered in this chapter, if the network is small (10 or fewer computers), it is generally easiest to start over with ICS than to troubleshoot it. Once you know you have removed any offending DHCP or DNS servers or any computers with static IP addresses, simply reconfigure ICS on the host computer, and then reconfigure and restart the other computers on the network.

Lesson Review

The following question is intended to reinforce key information presented in this lesson. If you are unable to answer this question, review the lesson materials and try the question again. You can find answers to the question in the “Questions and Answers” section at the end of this chapter.

A user has set up Internet Connection Sharing on a host computer that runs Windows XP but is experiencing problems with his clients being able to connect to both the Internet and other computers on the network. Which of the following items could be the cause of the problems? (Select all that apply.)

1. There is a DHCP server on the network.

2. There is a DNS server on the network.

3. There are computers on the network with static IP addresses.

4. There is a Windows 2000 server on the network.

Lesson Summary

• Internet Connection Sharing lets one computer with an Internet connection share that connection with other computers on the network. It is a good option for sharing a single Internet connection among a small number of computers.

• The computer running ICS always configures itself with the IP address 192.168.0.1. That computer also acts as a DHCP server and gives other computers on the network addresses in the 192.168 range.

• Troubleshooting ICS is fairly tricky, and the best option is almost always to reconfigure ICS on the network.