Troubleshoot Networking Problems in Windows XP
Published: September 19, 2005
In this column, I originally intended to answer a few of the many questions that I receive through e-mail and that I see regularly on the public newsgroups and in the community. But what I realized as I sat down to write was that given the constraints of an article (both space and its non-interactive nature), I couldn't realistically answer even a fraction of these questions. So, I decided instead to teach you how to solve networking problems yourself.
Computer networking remains the single largest source of questions I receive. In most cases, I couldn't answer these questions without actually sitting down at the person's computer and doing a little troubleshooting. I can't be at your computer, so I'll bring you to mine and show you what I do when I troubleshoot a network problem.
In this column, I show you how to troubleshoot:
| • | Physical network problems |
| • | Configuration problems |
| • | Software-interaction problems |
Troubleshooting basics
Successful troubleshooting requires a logical, consistent approach that seeks to narrow down the source of a problem by figuring out what is and isn't working until a single cause is identified. If you need to change something, change only one thing at a time. Trust me: The shotgun approach to troubleshooting is a bad idea. If you change two or three things all at once, restart your computer, and discover that it isn't working, you can't actually know whether one change alone could have solved the problem only to have another change break it again or break something else. So, be patient. Work through the process one step at a time.
Another good idea is to take notes as you work. I do this, and it can really help you keep track of exactly what has changed and what the result was. I use my Tablet PC to take my notes: I just open a new Microsoft Office OneNote tab for the session and jot down notes as I work. In this way, I not only have a record of exactly what I changed and the result of the change, but I also have a permanent record that I can combine with other troubleshooting sessions to help me understand the common problems I’ve faced and their solutions. With luck, these notes will help fix problems more quickly in the future.
Whenever you're troubleshooting a networking problem, your problem will fall into one of three basic categories:
| • | Physical. An underlying problem with cabling, a bad hub, or the like |
| • | Configuration. A problem with the configuration of one or more of network components |
| • | Software. A failure of the one of the pieces of software involved, an undesired interaction between two or more applications, or, potentially, an undesired piece of software that has been introduced into the network |
I've listed these categories in the order you should attack them—from the simple to the complex. Let's look at how to troubleshoot problems in each of these areas.
Troubleshooting physical network problems
When you experience network troubles, begin by checking the physical network devices and connections. In my experience, about 25–30 percent of all networking problems result from problems with the physical network. These problems are also the most easily fixed.
Make a thorough physical inspection of your network. Is the router plugged in? Have you accidentally substituted a cross-over cable for a regular network cable? Are all the network cables in good condition and well seated? Has the dog been chewing on your network cable? (Don't laugh: I spent an hour trying to troubleshoot a network problem on my home network only to discover that the culprit was Wally, shown in Figure 1.)
Make sure your dog doesn't chew on the network cable!
Microsoft Windows XP can help you see if a network cable is unplugged. As shown in Figure 2, if your cable is completely unplugged, this status appears in your Network Connections window. But a cable that is damaged or partially removed may not appear as disconnected.
Unplugged cable status in Network Connections
Be sure to monitor the lights on your router, hub, or the network adapter or port on your computer. These give you a good indication of your connection status as well as the connection speed.
Try changing the port your network cable is plugged in to on the hub or router. A bad port can be challenging to troubleshoot and identify.
The most important things you can do here are look and touch. Often, just reseating the cable into the plug is all it takes. But also learn what your network devices look like when they are working so that when you have a problem, you'll be able to see what's different.
Troubleshooting configuration problems
When you're sure that all your hardware is working correctly, begin sorting through your networking configuration. Most networking problems fall into this category: Approximately 60–70 percent of all networking problems that I've had to resolve concern a configuration problem of some sort. The good news is, configuration problems don't require you to crawl around on the floor under your desk with a flashlight. The bad news is, they take time and patience to resolve. Definitely take notes here! And before you do anything at all, set a system restore point on all the computers that you may need to change. Then, you have a way to start over if you need to.
The first step is to identify the current configuration of each computer on your network and write it down. You can retrieve this information in several ways, but the simplest method is to use the command-line program Windows IP Configuration (ipconfig). Simply type ipconfig at a command prompt, as shown in Figure 3.
Running ipconfig
This program tells you a lot about a computer's networking configuration, but if you want even more detail, type ipconfig /all. Run this program on all your computers, and write down the details so that you can compare them side by side. Look at the results shown in Figure 3: The computer shown has an IP address of 192.168.50.152, a subnet mask of 255.255.255.0, and a default gateway of 192.168.50.2. Now, for troubleshooting purposes, you don't actually care what any of these numbers are or what they mean. What you do care about is that they are all consistent across the network. So, the first number is the actual address: This address must be unique for every computer on the network, or you'll have a problem. However, the addresses should be similar and share a common base network address. The subnet mask identifies the base network address portion of the IP address.
Most subnet masks for home networks consist of 4 numbers of either 255 or 0. If a number in the subnet mask is 255, that corresponding number in the IP address is part of the base network address. For all the computers to communicate, they should all be using the same subnet mask and the same base network address.
For example, if the subnet mask is 255.255.255.0, the base network address consists of the first three numbers of the address and all the IP addresses should have the same first three numbers, as shown.
Tip: Base network address
On my network, I use 192.168.50 as my base network address, but your network will probably be different. Most likely, if you're using an Internet gateway or router, it will be 192.168.0 or 192.168.1, because these are the default base network addresses for the two most common routers out there. Another common base network address is 10.0.0. Don't worry, and certainly don't try to change the defaults on your router unless you have a good reason to. It's always easier to stick with the defaults when you can. |
The most common problem at this stage is that shown in Figure 4. One of the computers—usually one that is connecting wirelessly—shows an address that starts out 169.254.
A computer on the network can't retrieve a network address
When this happens, it means that the computer couldn't retrieve a network address from a Dynamic Host Configuration Protocol (DHCP) server (typically your router) and therefore automatically assigned itself an address from the base network address 169.254. This would be fine if all the computers your network were using addresses from the 169.254 base network address. If one of them isn’t, however, that computer will have problems connecting to the other network computers.
So, why didn't one computer get an IP address from the DHCP server? If the computer connects wirelessly, it almost always means that something is wrong with the Wired Equivalent Privacy (WEP) or Wi-Fi Protected Access (WPA) settings on your wireless router or access point. See Barb Bowman's columns on wireless networking or her recent Expert Zone Support Webcast: How to set up WPA-based wireless security on a home network for help.
If the computer isn't wireless but uses an Ethernet cable, the problem is back to a physical network issue. Check your network cabling again. For more on resolving common network problems with a router on your network, see my earlier networking column, Resolving Home Networking Issues.
If all the IP addresses are in the same base network address but one computer can't see the others on the network using My Network Places, chances are it's a computer browsing problem. See my home network troubleshooting column, Troubleshooting Home Network Issues for more information.
Troubleshooting software-interaction problems
If the physical network is fine and your basic configuration looks right, it's time to think about a software problem. The most common software problems are related to firewalls, so the place to start troubleshooting is with Denny Atkin's excellent column, Help Keep Your Computer Safe Using Windows Firewall.
Many third-party antivirus programs, such as Trend Micro's PCCillin or Norton AntiVirus, include built-in firewalls. You may not realize that you installed the firewall component when you installed the antivirus software, and now that firewall is getting in the way of connectivity on your home network.
To troubleshoot software problems, your first step is to disconnect your network from the Internet so that you can safely disable any firewalls or antivirus software while you troubleshoot. If you're using a router, disconnect it from the Internet. If you're using Internet Connection Sharing and a DSL or cable modem, unplug the modem.
After you're off the Internet, the second step is to disable any antivirus or firewall programs you have, including Internet Connection Firewall or Windows Firewall, on all the computers that are having problems. If this step solves the problem, you know that you've got a problem with one of these Windows features or products. So, it's just a matter of time and patience, carefully enabling one at a time and seeing when things break again. When they do, you know where the problem is, and you can either replace that product with one that doesn't cause problems or change the program's configuration to resolve the problem. When you've got everything working, don't forget to reconnect your devices to the Internet. And always restart all your computers after any round of network troubleshooting.
That's all I have space for this time, but for more information, check out my previous columns. The Microsoft Help and Support site for Windows XP also provides great tools and assistance. But most importantly, I strongly urge you to take advantage of the great Windows XP community that is out there. I've provided links to some community sites that I like and use, but there are many more. A good place to start is always the Windows XP Expert Zone, where we try to highlight a wide range of community sites.
Contact me
If you use Windows XP or Tablet PC and you have a topic you'd like me to cover in a column, feel free to write me at Charlie@mvps.org. I really want to hear what you think and the interesting ways you've found that a Tablet PC makes your work better.
Please understand that it is impossible for me to acknowledge or answer individual e-mail messages, nor can I provide individual technical support through e-mail. If you have a question or a problem, please ask it in the appropriate Microsoft public newsgroup or community, where all can benefit from the discussion. I regularly participate in the Windows XP Tablet PC Edition newsgroup, the Microsoft Security Homeusers newsgroup, and the Windows 64bit Edition newsgroup, among others. I look forward to seeing you there.
