Policy to control the frequency of Windows XP client DFS queries

Every 15 minutes, Microsoft Windows 2000 and Microsoft Windows XP domain member Distributed File System (DFS) clients query their domain controllers. This article discusses the registry and Group Policy Object (GPO) settings for the configuration of DFS name discovery on Windows XP domain members.

Windows client computers perform periodic discovery of domains and trusted domains in the forest. This discovery process runs against a domain controller from the domain that is hosting the client's computer account. This discovery process allows the Windows shell to more quickly distinguish queries for fully qualified domain names from fully qualified computer names.

For example: The results of the discovery process are cached in a special table to avoid real time queries to domain controllers in the domain. You may need to modify this discovery process in the following types of environments:

• Branch office environments in which the DFS client discovery increases the number of dial-on-demand events or wide area network (WAN) link uptime.
• Environments in which the many domain members that are issuing periodic queries create an excessive load on the domain controllers. For example, consider the following situation:
  A domain with 100,000 clients in which each client performs four queries per hour. Divide the number of queries performed by the number of domain controllers within the domain:
  
  (100,000 clients X four queries per hour)/N (where N is the number of domain controllers in the domain)

Controlling Client DFS Discovery

There are two methods for controlling the client DFS discovery behavior, the "legacy" method and the new method.

Legacy Method

The legacy method is a registry setting: Note The value is specified in minutes and cannot be less than 15 minutes.

New Method

For the new method, use a GPO or a registry value. This sets how often a DFS Client discovers domain controllers.

GPORegistry In the new method, you can enable the DFS discovery interval in the GPO; thus, you can apply the discovery interval to specific Organizational Units (OU) that are hosting the computer accounts of interest, or on the root of the domain to affect all domain members.

Windows XP clients dynamically check for updates to the DFS discovery interval. The valid range for DfsDcNameDelay is 15 to 360 minutes. No reboot is required for new settings to take affect.

Windows XP Client DfsDcNameDelay Value Processing

1. Upon startup, the policy key for DFS name discovery interval is checked. If you do not specify a policy key value, the client checks the legacy registry key. If neither key contains a value, the client defaults to initiating the DFS discovery process every 15 minutes. Every 15 minutes the client also checks for a new policy or legacy value.
2. If you set either registry value to an invalid value, the default 15 minute setting is used.
3. If the GPO specifies a valid value, the client initiates the discovery process at that interval. The client will not check for new policy or legacy values until the next GPO refresh interval.

NOTES

• Environments that contain mature domains and trusted domains may decrease the refresh interval up to its maximum value (360 minutes or 6 hours).
• You can view and flush the contents of the special table (the results of the discovery process), which consists of domains and trusted domain names, by using the following two commands:
  dfsutil /spcinfo
  dfsutil /spcflush

For more information about DFS name discovery, click the following article numbers to view the articles in the Microsoft Knowledge Base: