Windows 7 / Networking

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Troubleshoot DNS

DNS is an essential resource for name resolution. When something goes wrong with DNS, it can have far-reaching effects in your network. An understanding of how to troubleshoot DNS can be incredibly valuable. The thing you will love about DNS is that your ability to troubleshoot DNS is directly associated with your understanding of basic DNS operations and the specific DNS configuration you are working with.

With a good understanding of DNS and a strong understanding of your network, you are well positioned to deal with most of the issues that will crop up in DNS. One of the really good things about DNS is that although there are occasional problems that fall outside the realm of what is considered normal, most of the problems are seen over and over again in networks that are running DNS and are fairly easy to isolate and fix.

When you are trying to troubleshoot a problem in DNS (or anywhere else in your network, for that matter), you should use a root cause analysis approach. What exactly is root cause analysis? It can be described with a single sentence:

Discover the problem before you "fix" anything.

When troubleshooting DNS, you will notice that problems seem to fall into four categories:

• DNS clients
• DNS servers
• Dynamic updates
• Zone problems

As you encounter an issue with DNS, begin by trying to isolate the source of the problem. You will find that the majority of the time the problem will easily fit into one of these four categories. If it doesn't, don't worry-all is not lost. You can keep working to identify the source of the problem.

The most common problems with DNS servers are actually not really problems with the DNS servers at all; they are hardware- or networkrelated. For example, say your users suddenly flood your help desk with calls indicating they cannot "find" anything on your network. Shares are unavailable, the Internet seems to be down, and some cannot even log in. This sounds like a DNS problem. It is! Where does it fit among the four categories? It sounds like a DNS server problem. At this point, you can begin troubleshooting by checking the physical hardware that supports the DNS server. Is everything actually plugged in and working? You notice that the network cable that connects your DNS server and its network interface card has been laying across a sharp steel beam on top of your server rack, and the weight of the other cables has somehow managed to sever this one. You put in a new cable, and in minutes the network is up and running. Don't just assume that the hardware is fine and move on to other things. Check it out. Many, many times a simple hardware fix is all that is necessary.

If the hardware checks out, then you can start going down your check list of items to identify the problem and then apply the solution. Microsoft maintains a troubleshooting tool specifically for DNS. It is excellent! Not surprisingly, it is broken down into four categories. The vast majority of DNS issues can be solved by using these simple troubleshooting tools. They provide a great level of detail and solutions at each step of the process to help you not only identify the problem but also fix the problem.

The vast majority of DNS issues will be within your troubleshooting reach if you use the tools discussed in the previous section. If you run into a problem that you cannot solve quickly on your own using the troubleshooting tools, then use other resources at your disposal. The Internet can be a great source of information to help you isolate your problem and find a solution. If you have any kind of support contacts, use them. Support incidents on the phone or in person may make sense if you have exhausted your knowledge without finding a solution. The key is not to give up. Use your root cause analysis skills and your understanding of the environment to find and fix the problem.