DNS Server Stops Using Round Robin for Host Name Resolution

After you install Windows 2000 DNS or after you apply the latest Dns.exe, your Microsoft Windows NT Domain Name Service (DNS) server no longer responds to queries in a round robin fashion.

For additional information, please see the following articles in the Microsoft Knowledge Base:

ARTICLE-ID: 159310  (http://support.microsoft.com/kb/159310/EN-US/ )
TITLE : Updated Version of Dns.exe Fixes Several Problems

ARTICLE-ID: 168321  (http://support.microsoft.com/kb/168321/EN-US/ )
TITLE : Creating a DNS Record for a Host That Has 2 or More IP Addresses

The latest version of Dns.exe for Windows NT and Windows 2000 DNS server introduce a new feature, LocalNetPriority, that attempts to return Host resources that are local to the requestor instead of merely responding round robin.

Windows NT 4.0 Servers

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

By default, this feature is enabled and normal round robin responses will not occur. To return to round robin responses, you will need to use the following steps to disable the LocalNetPriority setting:

1. Start Registry Editor (Regedt32.exe or Regedit.exe).
2. Go to the following subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DNS\Paramete
3. Create a new value using the following information:
   Value Name: LocalNetPriority Data Type : REG_DWORD Data : 0 (0 = disabled, 1 = enable
   
   NOTE: This value does not exist by default.
4. Stop and restart the Microsoft DNS server service.

Windows 2000 Servers

By default, this feature is enabled, and normal round robin responses will not occur. To return to round robin responses, use the following steps to disable the LocalNetPriority setting:

1. Open the DNS Management Console in Administrative Tools.
2. Right-click servername, and then click Properties.
3. Click the Advanced tab.
4. Clear the Enable Netmask Ordering check box.

The DNS server will attempt to offer the "best-fit" address in response to a DNS query. This best-fit is one that is determined to be on the same subnet as the requesting DNS Client.

The classfull address is used to determine if the record and the querying DNS Client are on the same subnet. This means only the first octet will be used for class A addresses, the first two octets for class B, and the first three octets for Class C addresses. If you have subnetted your address space, this may have a derogatory effect on round robin load balancing.