Windows 7 : Troubleshooting Your Network - Testing Network Cables , Checking Network Configuration

1. Testing Network Cables

If your computer can’t communicate with any other computer on your LAN, and the Device Manager doesn’t indicate a faulty network card, you might have a wiring problem. Wiring problems can be the most difficult to solve because it’s difficult to prove that data is leaving one computer but not arriving at another. 

If your network uses UTP cabling plugged in to a hub, there’s usually a green LED indicator on each network card and at each port on the hub. Be sure that the lights are on at each end of your network cable and those for the other computers on your LAN.

You also can use inexpensive (about $75) cable test devices that check for continuity and correct pin-to-pin wiring order for UTP wiring. They come as a set of two boxes. One gets plugged in to each end of a given cable run, and a set of blinking lights tells you whether all four wire pairs are connected and in the correct order. (If you install your own network cabling and/or make your own patch cables,.)

2. Checking Network Configuration

If hardware isn’t at fault, you might 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.

In the Command Prompt window (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 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 (ICS), 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 your IP address starts with the numbers 169.254, 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; perhaps you’ve just connected a few computers so you can share files and printers. However, if you expected to get Internet access through your network—that is, if you use ICS or a hardware Internet connection router, or you have a more complex network with a DHCP server—this is a serious problem. Restart the connecting sharing computer or the router, and then restart your computer and try again.

• Network Mask— This is usually 255.255.255.0, but other settings are possible. 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 computer’s identification and workgroup or domain membership setup from the Computer window. To do so, click Start, Computer. Look at the bottom of the screen for the computer name and domain or workgroup name, as shown in Figure 1.

Figure 1. Your computer’s name and workgroup or domain membership are 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-hbmyvpc-hb.mycompany.com on a domain network) and the domain name. Your domain name might not include .com. It might say .local instead or 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. would be called

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, Control Panel, View Network Status and Tasks (under Network and Internet), Change Adapter 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, use the ipconfig command, described earlier, to check the settings.