U-Tools: Unique Tools for Windows System Administrators
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Configuring DNS

The Domain Name System (DNS) is an Internet standard for mapping Internet computer names (called “host names”) to numerical Internet Protocol addresses (called “IP addresses”). The DNS server contains a database of all of the host names for a domain.

Active Directory uses DNS to locate the domain controllers in a domain.

Note: Incorrect configuration of DNS is the number one cause of problems with Active Directory. If DNS is configured incorrectly, domain controllers will not be able to locate each other for replication. Client computers will not find their domain controller(s), and users will not be able to log on.

A domain controller uses DNS to connect back to itself. If DNS is incorrectly configured, the domain controller will not be able 'see' itself, causing loopback errors that will prevent the DC from connecting to its own local AD database.

U-Move moves all DNS settings by default

Because DNS is critical for Active Directory, U-Move is careful to move all DNS settings from the source computer to the destination computer when cloning AD. This includes the following:

  • Client DNS settings
  • Server DNS settings
  • Server DNS zone data files (\Windows\system32\dns\*)
  • Hosts and lmhosts text files (\Windows\system32\drivers\etc\*)

By moving all DNS settings, U-Move prevents potential DNS errors due to differences in the DNS settings between the old and new computers.

Option: Skip moving the Client DNS Settings

If you choose do not copy the IP addresses, U-Move will skip moving the client DNS settings, the hosts file, and the lmhosts file from the old computer to the new computer This can be useful when moving AD to another network (such as the cloud).

U-Move will display the current client DNS settings and ask you to review and confirm them during the interview.

Types of moves: Clone versus Upgrade

When cloning AD using an emergency move or a planned move, the DNS settings and zones will carry over transparently to the new computer. The only issue is re-registering dynamic DNS records written more than 7 days ago (see below).

When upgrading AD (swing migration), the DNS settings and zones will carry over transparently to the new computer.

When cloning AD to an isolated test lab, you need to consider additional issues (see below).

Troubleshooting DNS Problems

To troubleshoot DNS run Dcdiag to verify DNS connectivity:

dcdiag /v /test:DNS

The following is an example of a successful run of Dcdiag:

Directory Server Diagnosis

Performing initial setup:
   Trying to find home server...
   Home Server = MyServer
   * Identified AD Forest.
   Done gathering initial info.

Doing initial required tests

   Testing server: Default-First-Site-Name\MyServer
      Starting test: Connectivity
         ......................... MyServer passed test Connectivity

Doing primary tests

   Testing server: Default-First-Site-Name\MyServer

      Starting test: DNS

         DNS Tests are running and not hung. Please wait a few minutes...
         ......................... MyServer passed test DNS

   Running partition tests on : ForestDnsZones

   Running partition tests on : DomainDnsZones

   Running partition tests on : Schema

   Running partition tests on : Configuration

   Running partition tests on : MyDomain

   Running enterprise tests on : MyDomain.com
      Starting test: DNS
         Test results for domain controllers:

            DC: MyServer.MyDomain.com
            Domain: MyDomain.com

         Summary of test results for DNS servers used by the above domain

         Summary of DNS test results:

                                            Auth Basc Forw Del  Dyn  RReg Ext
            Domain: MyDomain.com
               MyServer                         PASS PASS PASS PASS PASS PASS n/a

         ......................... MyDomain.com passed test DNS

If Dcdiag reports a failed DNS test, you should first check network connectivity with the DNS server. Use the commands ping and nslookup to verify that the DNS server is visible on the network and can resolve the DNS records.

Not all failed DNS tests indicate errors. For example if you are running AD on an isolated network for offline testing in your lab, Dcdiag will fail the DNS test because there are no DNS forwarders that can reach the Internet. This is normal and expected.

Another common failed DNS test is the lack of a reverse PTR record. PTR records are optional; many sites to not configure them. PTR errors are normal and can be ignored.

Troubleshooting: The DNS Client service

The DNS Client service caches results from the DNS service. This includes “negative” results where an address is not found. You should flush the cache of the DNS Client service before troubleshooting any changes to your DNS configuration:

ipconfig /flushdns


To assist you in troubleshooting DNS problems, upon each boot the domain controller will write a copy of its desired DNS records to a text file. The text file is named C:\Windows\System32\config\netlogon.dns. You can inspect this file (use NOTEPAD.EXE) in order to verify that your DNS server contains the correct A, PTR, and SRV records for the domain controller.

If your DNS server does not contain the records listed in netlogon.dns, you need to find the cause and correct it. If you are using dynamic DNS updates, you need to investigate why the domain controller failed to update the dynamic records (for example, the NIC has the wrong DNS client IP address). If you are using static DNS, you may need to manually recreate the necessary A, PTR, and SRV records.

The DNSLint Utility

The DNSLint tool can be used to diagnose DNS errors. On the moved domain controller type the command
dnslint /ad /s localhost /v

Immediate re-registration of DNS records

If you see errors in the Event Log due to problems with locating a domain controller in DNS that has failed to dynamically register its DNS address, and you do not want to wait 5-10 minutes for automatic re-registration, you can force the domain controller to immediately register its IP address with the DNS server. Open an administrative console and type the following commands:

ipconfig /flushdns
ipconfig /registerdns
nltest /dsregdns

The ipconfig command will tell the computer to send ("register") its DNS A and PTR records to the DNS server. The nltest command will register the SRV records. The SRV records are used to locate domain controllers.

Ipconfig and Nltest are built-in utilities.