Troubleshooting DNS

Many of the DNS problems that a network administrator encounters result from missing or incorrect resource records. There are several different tools available that can be used to troubleshoot problems with resource records. These include the following:

• Nslookup

• Dnslint

• Dnscmd

You can run NSLOOKUP with an IP address for a system that you know is outside of your local LAN, or an address that would normally be handled by DNS. NSLOOKUP does the reverse of standard DNS, and should tell you the FQDN that DNS is returning for that particular IP address. If it fails to do so, you need to check DNS connectivity by PINGing the DNS server from a client. You also need to check and make sure that the results of NSLOOKUP are actually valid and true; if they're not, there's a problem with the DNS database and requires some reconfiguration.

NSLOOKUP can be run in two different modes: interactive and noninteractive. If you are looking for a single piece of information, use NSLOOKUP in noninteractive mode. For example, type NSLOOKUP 192.168.0.1 to find the name of the computer. If you need to look up more than one piece of information, use interactive mode.

The Dnslint command-line utility is included in the support tools. It is used to verify the existence and consistency of DNS records. For example, if clients are unable to log on to an Active Directory domain, you can use the command-line utility to verify the existence and the accuracy of the SRV records.

Dnslint will verify the following information and generate a report in HTML format:

• Verifies that all authoritative DNS servers for a domain are responding to queries.

• Verifies that all authoritative DNS servers have synchronized zone data.

• Verifies resource records associated with delegation.

Dnscmd is another command-line utility included in the Windows Server 2003 support tools. It can be used to perform various DNS administrative tasks from the command prompt window. You can use the command to perform the following tasks:

• View and change the properties of a DNS server, zone, or resource record.

• Create and delete zones and resource records.

• Force replication events.