DNS Troubleshooting

In business or enterprise class computer network infrastructures, a well designed DNS name resolution is very essential within the organization. And one of the most common internet access problems is caused by the failure of DNS name resolution. The inability to resolve DNS names can bring clients activities to a standstill. The ability to perform DNS Troubleshooting is very essential for the network administrators.

Basically there are two possible causes when clients cannot resolve name resolutions: either the client is incorrectly configured, or the DNS server itself is inaccessible or not functioning properly. How can we perform a DNS troubleshooting?

Troubleshooting Client Configuration Problems

It is common that the users find the error message something like “Name Not Found” when accessing the TCP/IP resources such as Internet access. This is a common DNS resolution problem, and the first order to do the DNS troubleshooting is to determine whether the computer has any TCP/IP connectivity at all. You need to make sure that the computer is properly connected to the network with the correct IP address configuration. The common method to make sure that you properly connected to the network is to “ping” to one of the server using the IP address instead of its DNS name. If you find that the server is accessible by using the IP address, then you know that the problem is related to the name resolution process.

Next step is to check the client computer’s TCP/IP configuration parameters. If the client is running Windows platform (2000, XP, or Vista), in command prompt type ipconfig /all and press Enter to view the computer’s TCP/IP settings including the IP address, subnet, default gateway and DNS setting. Check the DNS setting if the IP addresses are correct for the clients on that network segment. Ping the DNS server by using the IP address and see if it fails.

But if the clients within the organization should use DHCP server, make sure that the DHCP is enabled in the clients by configuring the TCP/IP property to obtain the IP address automatically. If the test fails, then it could be either the DNS server is not running at all, or a network connectivity problem. See also troubleshooting the network connectivity for more detail information. But if you find that the computer can access the network and DNS setting is configured correctly, there should be problem elsewhere in the network.

Troubleshooting DNS Server Problems

There are many conditions that cause the DNS server to function improperly. The following DSN troubleshooting will help you to localize the cause of the problems.

Non-Functioning DNS Servers

You have assured that there is no problem with the client configuration and no problem with the network connectivity, there must be problem with the DNS server itself. There should be either connectivity problem or improper configuration. You should start reviewing the TCP/IP configuration. DNS server should have the static IP address, and this address must be excluded from the DHCP IP address zone. You can use the same ipconfig /allcommand to view the DNS server’s IP address and other TCP/IP settings, whether or not they are assigned by DHCP.

If the clients can ping the DNS server using the IP address, but cannot receive replies to name resolution requests, the problem could be that the DNS Server service is not running.

Check the services from the DSN console and see if it is running. Also make sure that DNS service setting in the startup type selector is set automatically on server booting. If the startup Type selector for the DNS Server service is Automatic and the service is not running, there must have been someone stopped it or there is a problem that caused it to stop. You can review the event viewer logs to see what the root of the problem is.

Now, start the services and make a test and see if it is functioning properly.

Troubleshooting Incorrect Name Resolutions

In some cases, the client computers might receive the outdated or incorrect information from the DNS server. This condition could be caused by any of the following:

1. Incorrect resource records. Typically this is caused by the possibility of typographical errors if the DNS records are modified manually. Check the records manually and correct them in the server.
2. Dynamic update failure. If you configured the DNS server to use dynamic update, the incorrect or outdated IP addresses of the DNS records can be caused by the dynamic update failure. The client computers can issue an ipconfig /registerdnsat a command prompt to update the record. ipconfig /registerdns is used to allow the client to re-register its IP address with the DNS server. And make sure to review the DNS servers if they support the dynamic update.
3. Zone transfer failed. The record database in a secondary DNS server can be outdated if the zone transfer is failed or the configured zone transfer interval is long enough. In this case you can manually trigger a zone transfer. Different compression formats or unsupported resource record types can also cause the failure of zone transfer. The best practice can also be done by clearing the cache. See also further discussion about DNS forwarding.

In some cases, a DNS server can successfully resolve names for which it is the authority, but fails to resolve names in other domains. This is typically caused by the recursion failure where the server does not forward the queries to the appropriate server or probably do not forward the queries at all. This is probably caused by the incorrect root hints configuration. The root hints contain DNS server’s list of root name server addresses, which are used to resolve names outside its domain. For Windows server 2003, the DNS server comes with preconfigured root hints for the Internet root name servers.

Reference: Microsoft.Com

See also:

• Understanding Virtual LAN – a basic concept
• Understanding the WAN technologies – types of WAN services
• Understanding many types of LAN topologies
• How to tweak DNS setting to speed up internet connection
• How to share the Internet connection