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This chapter is from the book

Checking Network Configuration

If hardware isn't at fault, you may have a fundamental network configuration problem. Often the Event Log or Device Manager gives these problems away, but if they don't, you can use another batch of tools to check the computer's network configuration.

ipconfig

If your computer can't communicate with others on your LAN, after you check the Event Log and Device Manager, use the ipconfig command-line utility to see whether your computer has a valid IP address. Check other computers on the LAN, too, to ensure that they do as well.

At the command prompt (which you open by choosing Start, All Programs, Accessories, Command Prompt), type the following command:

ipconfig /all

The results should look something like this:

Windows IP Configuration
   Host Name . . . . . . . . . . . . : myvpc-hb
   Primary Dns Suffix  . . . . . . . : mycompany.com
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : Yes
   WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Local Area Connection:
   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Intel 21140-Based PCI Fast Ethernet Adapter
   Physical Address. . . . . . . . . : 00-03-FF-DD-CA-5F
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::ed10:dff9:693c:803d%8(Preferred)
   IPv4 Address. . . . . . . . . . . : 192.168.15.108(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Lease Obtained. . . . . . . . . . : Friday, October 20, 2006 5:55:11 PM
   Lease Expires . . . . . . . . . . : Friday, October 27, 2006 5:55:23 PM
   Default Gateway . . . . . . . . . : 192.168.15.1
   DHCP Server . . . . . . . . . . . : 192.168.15.1
   DHCPv6 IAID . . . . . . . . . . . : 201327615
   DNS Servers . . . . . . . . . . . : 192.168.15.1
   NetBIOS over Tcpip. . . . . . . . : Enabled

(Unless you're troubleshooting IPv6 Teredo connections, ignore the parts that mention Tunnel adapters.)

The most important items to look for are the following:

  • Host name—This should be set to the desired name for each computer. If you can correspond with some computers but not others, be sure that the ones that don't work are turned on and correctly named. Make sure that you don't have two computers with the same name, and that none of the computer names is the same as the workgroup name.
  • IP address—This should be set appropriately for your network. If your LAN uses Internet Connection Sharing, the address will be a number in the range 192.168.0.1 through 192.168.0.254. If your LAN uses DHCP for automatic configuration, your network manager can tell you whether the IP address is correct. Networks with cable/DSL sharing routers usually use numbers starting with 192.168.x where x is a number from 0 to 15.

    If you see a number in the range 169.254.0.1 through 169.254.255.254, your computer is set for automatic configuration, but no DHCP server was found, so Windows has chosen an IP address by itself. This is fine if your LAN uses this automatic configuration system. However, if there should have been a DHCP server, or if you use Internet Connection Sharing or a hardware Internet Connection router, this is a problem. Restart the ICS computer or the router, and then restart your computer and try again.

  • Network mask—This usually looks like 255.255.255.0, but other settings are possible. At the least, all computers on the same LAN should have the same network mask.

Each computer on the same LAN should have a similar valid IP address and the same network mask. If they don't, check your network configuration. The built-in Windows "Repair" function may also be used to help fix problems with DHCP-based (automatic) IP address assignment.

Computer

You can check your computer's identification and workgroup or domain membership setup from the Computer window. To do so, click Start, Computer. Look in the Details pane at the bottom of the screen for the computer name and domain or workgroup name, as shown in Figure 24.5.

Figure 24.5

Figure 24.5 Your computer's name and workgroup or domain membership is displayed at the bottom of the Computer window.

On a Windows Workgroup network, the workgroup name should be the same on all computers on your workgroup LAN. All of the computer names must be different from each other.

On a Windows domain network, you should see your computer's name displayed as part of a Windows domain name (for example, my computer named myvpc-hb would be called myvpc-hb.mycompany.com on a domain network) and the domain name. Your domain name might not include .com. It might say .local instead, or may use a different ending. In any case, be sure that your computer is actually a domain member. If the word "workgroup" appears instead, your computer is not a domain member and will not be able to use domain logins or some domain resources.

Network Connections

You can manually check all installed network protocols and services and their configuration by viewing Network Connections and viewing the properties for Local Area Connection. To view this screen, click Start, Network. At the top of the Network window, click Network and Sharing Center. In the left pane of that window, click Manage Network Settings. Then, right-click your Local Area Connection icon (or the appropriate wireless connection icon) and select Properties.

Confirm that each required protocol is installed and correctly configured. In general, the settings on each computer on your LAN should match, except that the IP address differs (usually only in the last of its four dot-separated numbers). If your LAN uses Automatic IP address configuration, you need to use the ipconfig command, described earlier, to check the settings.

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