Lesson 6: Troubleshooting the DNS Service

This lesson discusses how to troubleshoot name servers by using the DNS monitoring and logging options and the Nslookup command-line utility.

DNS has an option that allows you to monitor the DNS Service. In the DNS tool, right-click the name server to monitor, click Properties, and then click the Monitoring tab. Test the name server by performing two types of queries:

• A Simple Query Against This DNS Server. Select this option to perform a simple query test of the DNS server. This will be a local test using the DNS client on this computer to query the name server.
• A Recursive Query To Other DNS Servers. Select this option to perform a more complex, recursive query test of the name server. This query tests the name server by forwarding a recursive query to another name server.

The DNS tool allows you to set additional logging options for debugging purposes. Right-click the name server, click Properties, and then click the Logging tab. You can select from 11 options: Query, Notify, Update, Questions, Answers, Send, Receive, UDP, TCP, Full Packets, and Write Through.

Nslookup is the primary diagnostic tool for the DNS Service, and it is installed along with TCP/IP. Use Nslookup to view any resource record and direct queries to any name server, including UNIX DNS implementations.

Nslookup has two modes: interactive and noninteractive.

• When you require more than one piece of data, use interactive mode. To run interactive mode, at the command prompt, type Nslookup. To exit interactive mode, type exit.
• When you require a single piece of data, use noninteractive mode. Type the Nslookup syntax at the command line, and the data is returned.

The syntax for Nslookup is as follows:

nslookup [-option ...] [computer-to-find | - [server]]

Table 3.5 describes the optional parameters for Nslookup.

Table 3.5 Nslookup Optional Parameters

Syntax	Description
-option…	Specifies one or more Nslookup commands. For a list of commands, type a question mark (?) in interactive mode to open Help.
computer-to-find	If the computer to find is an IP address, Nslookup returns the host name. If the computer to find is a name, Nslookup returns an IP address. If the computer to find is a name and does not have a trailing period, the default DNS domain name is appended to the name. To look up a computer outside the current DNS domain, append a period to the name.
-server	Use this server as the DNS name server. If the server is omitted, the currently-configured default name server is used.

You can troubleshoot name servers by using the DNS tool for monitoring and logging options and the Nslookup command-line utility. You can test the name server by performing a simple query or by performing a recursive query. A simple query performs a local test using the DNS client on this computer to query the name server. A recursive query performs a more complex, recursive query test of the name server. This query tests the name server by forwarding a recursive query to another name server.

You also learned that Nslookup is the primary diagnostic tool for the DNS Service. It is installed along with the TCP/IP protocol. You can use Nslookup to view any resource record and direct queries to any name server, including UNIX DNS implementations.