The ipconfig /all command lets you easily view a computer’s connection information. If you know a little about TCP/IP (Transmission Control Protocol/Internet Protocol), you know that computers communicate on a network and over the Internet by using specific numbers called IP addresses, and these addresses distinguish them from other computers on the network. IP addresses are created from four sets of numbers, one to three digits each, such as 192.168.0.5.Each computer on a network must be configured with an IP address that is different from every other on the network, the same way a computer must have a computer name that is distinct. If you’ve created a home network (workgroup) using the Network Setup Wizard, these IP addresses were created automatically.
When performing advanced troubleshooting, you’ll want to verify that all IP addresses on the network have the same pattern of numbers. For instance, if the IP addresses of three of the four computers on the network take the form 192.168.0.x, where x represents a single-digit number, the other computer’s IP address must also follow that form. Again, each IP address must be distinct, which means in this example that x must be unique for each address. While IP addresses are similar but different, subnet masks are all the same. A subnet mask tells the computers who is on their network, and who is not. A computer with a different subnet mask from the others will not be reachable. An example of a subnet mask is 255.255.255.0.
When computers on a network can’t communicate, and you want to perform advanced troubleshooting, you can find out what IP address each computer has been assigned by using the ipconfig /all command. The information output by ipconfig /all may give you insight as to the problem. Figure 8-19 shows an example of the output. Notice the IP address and subnet mask for this computer.
To get this information and troubleshoot connectivity on the network, at each computer:
- Click Start | All Programs | Accessories | Command Prompt.
- At the command prompt, type ipconfig /all.
- Locate the IP address for the local area connection, generally under Ethernet Adapter. Verify that the IP addresses are all similar, 192.168.0.x, where x is unique for each so that there are no duplicate
addresses. - Locate the subnet mask for the local area connection, generally under Ethernet Adapter. Verify that the subnet mask for all computers is 255.255.255.0.
If you find a computer that does not have the correct IP address or subnet mask, you need to correct it. There are multiple ways to do this. One way is to run the Network Setup Wizard again. Another is to change the network settings in the Properties dialog box of My Computer:
- At each computer, right-click My Computer, choose Properties, and click the Computer Name tab.
- Note what each workgroup name is, and what each computer name is. On the computer that has been deemed the problem computer, click Change.
- In the Computer Name Changes dialog box, type in a new name for the computer if the name is not distinct on the network. Type in the correct workgroup name. Click OK.
- Click OK twice more, and then click Yes to restart the computer.
- Verify that you can reach network resources. If you cannot, run the Network Setup Wizard again on all computers. This will most likely not be necessary.