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Monitoring and Troubleshooting the DNS Server Service

The DNS snap-in not only lists dynamic updates resulting in host records for hosts on the network; the snap-in also provides you with a way to test the DNS server and monitor the results. Two different tests in the form of queries are available: a simple query and a recursive query.

To monitor and run these test queries, follow these steps:

1. Right-click the DNS name server in the DNS snap-in, and then select Properties from the shortcut menu that appears. The Properties dialog box opens for the DNS server.

2. Click the Monitoring tab to select it. Two check boxes are available on the tab (see Figure 15.13): a simple query against this DNS server and a recursive query to other DNS servers.

Figure 15.13. You can test the DNS server with queries.

3. Click the appropriate check box to set up the test (you can select both check boxes). Then click the Test Now button. The test results appear in the Test Results box of the Monitoring tab.

You can also monitor a DNS server over time with these query tests. Click the Perform Automatic Testing at the Following Interval check box and then set the time Interval in the Test interval box.

If your server fails one of these tests when they are performed periodically (if you set up for automatic testing), the server is marked with an alert icon (a triangle with an exclamation point on it). This lets you know when you view the Server icon in the DNS snap-in that there is a problem with the server.

Viewing DNS Events

You can view events related to your DNS server in the Server Manager window and the Windows Server 2008 Event Viewer. The Server Manager shows events related to the DNS server when you select the DNS Server node in the Node pane of the Server Manager window. Double-click any event to view the details of that event.

You can also use the Event Viewer to view DNS events. In the Server Manager window, click the Go to Event Viewer link on the right side of the Server Manager window.

Did you Know?

You can start the Event Viewer from the Start menu: Click Start, Administrative Tools, and then Event Viewer. The Event Viewer opens in the MMC.

The Event Viewer helps you to track a number of event logs related to your server’s performance, the network operating system, and the services installed on the server. Windows Server 2008 provides a new look for the Event Viewer, which provides a multi-paned snap-in that makes it easy to view details related to a selected event. For more about the Event Viewer and the type of information it provides in its log files (which operates in its own snap-in), see Hour 24, “Monitoring Server Performance and Network Connections.”

To view DNS log events, expand the Event Viewer node in the Server Manager node tree. Then expand the Applications and Services Logs and select the DNS Server icon. The events logged in this file appear in the Details pane (see Figure 15.14).

Figure 15.14. You can view the DNS-related events in the Event Viewer.

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If your DNS service is running smoothly, you will typically see only information events in the log. If you see Warning or Error icons, you might have a DNS problem (see Hour 24 for more about the types of events logged by the Event Viewer).

Using Nslookup

Nslookup is an excellent troubleshooting tool for DNS. Nslookup is a command-line utility, and you can use it to view host records, do query testing of DNS servers, and perform other tasks related to DNS from the command line.

You can use the nslookup command to find information such as the IP address of a particular host on the network. The command takes the syntax nslookup name1 name2, where name1 is the hostname for the host computer that you want to look up and name2 is the name of the DNS server that you want to query. Running these queries with Nslookup enables you to see whether the DNS server is dynamically recording the host records needed to resolve the queries.

Each time you run the nslookup command as described in the previous paragraph, you are returned to the command prompt. This is called the Nslookup noninteractive mode. If you want to run several Nslookup commands in succession, you can enter the Nslookup interactive mode.

Open a command window (Start, Run, type cmd, and then click Run). At the command line, type nslookup (with no additional parameters) and then press Enter. This command provides the default DNS server information and the IP address of the server. This also places you in Nslookup interactive mode (the command prompt is replaced by the Nslookup > prompt).

When you are in interactive mode, you do not have to type the nslookup command. The command syntax becomes name1 name2, where you supply the hostname (name1) to be resolved, followed optionally by the DNS server (name2) you want to query.

Did you Know?

When you want to exit Nslookup interactive mode, type exit at the Nslookup prompt (>) and then press Enter. You are returned to the command prompt.

Nslookup can also be used to verify that a forward lookup zone is configured correctly. Let’s look at how to run Nslookup at the command prompt.

To test that a forward lookup zone is configured correctly, use the following steps to simulate a zone transfer:

1. At the command prompt (click Start and then select Command Prompt), type nslookup and press Enter. This places you in interactive mode.

2. Type the command server ip address (where ip address is the IP address of the DNS server that you want to test). Then press Enter.

3. Use the set command to set the query type to any type of record: set querytype=any. Then press Enter.

4. To simulate the zone transfer type, use the command ls -d domain name, where domain name is the name of the forward lookup zone. Then press Enter.

If the zone is configured to allow zone transfers, you see the results of the “fake” zone transfer in the command prompt window.

Using the queries provided by the DNS snap-in, the Server Manager and Event Viewer DNS logs, and the nslookup command can help you stay on top of your DNS implementation. Even when you know that you have configured the DNS service perfectly, you should periodically use these tools to check your DNS implementation.

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