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How a slow link is detected for processing user profiles and Group Policy
Article ID: 227260 - View products that this article applies to.
This article was previously published under Q227260
NoticeThis article applies to Windows 2000. Support for Windows 2000 ends on July 13, 2010. The Windows 2000 End-of-Support Solution Center
(http://support.microsoft.com/?scid=http%3a%2f%2fsupport.microsoft.com%2fwin2000)is a starting point for planning your migration strategy from Windows 2000. For more information see the Microsoft Support Lifecycle Policy
This article describes how a slow link is detected in Windows 2000 for processing user profiles and Group Policy.
Windows 2000 includes a new method of determining whether a client computer is gaining access to a domain controller over a slow link to apply Group Policy or download a roaming user profile. This takes the form of a sequence of TCP/IP ping requests to the destination server. There is more reliance on the detection of slow links in Windows 2000 because this is used to determine the types of Group Policy that are applied.
The new mechanism takes the form of measuring the response time from a sequence of TCP/IP pings from the client computer to the server to determine the average transfer rate in kilobits per second (kbps). The client pings the server three times with 0 bytes and three times with 2048 bytes. If the response time from any of the pings is less than 10 milliseconds (ms), the link is automatically considered fast. Otherwise, the average transfer rate is calculated by averaging the differences between the first (0 byte) and second (2048 byte) ping times. If the transfer rate is slower than the default or a value that is defined by the administrator, the connection is considered slow.
Windows 2000 uses the following formula:
LinkSpeed=32000/ulTotalIn this formula, ulTotal is the average of the differences between the first and second ping times.
Consider the following example.
In this example, the difference between each time can be calculated in the following way:
First difference: 245-236=9
Second difference: 247-240=7
Third difference: 245-237=8
Therefore, ulTotal would be (9+7+8)/3 = 24/3 = 8. The estimated link speed would be 32000/ulTotal = 32000/8 = 4000.
Effects on Group PolicyWhen Group Policy is applied to the computer or to the user, the IP slow link detection mechanism is always used. By default, if a slow link is detected, some forms of Group Policy are not applied. For more information about which Group Policy components do not apply, and about how to modify this behavior, click the following article number to view the article in the Microsoft Knowledge Base:
227369The administrator can specify the connection speed independently for the application of Group Policy to computers and users:
(http://support.microsoft.com/kb/227369/ )Default behavior for Group Policy extensions with slow link
Effects on roaming user profilesRoaming user profiles are not required to be stored on a server on which TCP/IP is an installed protocol. However, when a user tries to download a roaming user profile, the IP slow link detection mechanism is used first. If Windows 2000 detects that the server on which the roaming user profile is located does not support TCP/IP, it uses the method that is used by Microsoft Windows NT 4.0 and earlier versions. In this method, the time that it takes for the server to respond to a request for the file attributes of the profile is timed and compared to the value determining a slow network.
The administrator can specify the connection speed that determines a slow network when user profiles are being downloaded:
Viewing the slow network detection data in the debug logIf debug logging is enabled on a Windows 2000-based computer, the result of the slow network detection mechanism is recorded in the Userenv.log file. An example of the entries recorded when a client is on a fast link (where the TCP/IP pings resulted in times of less than 10 ms) might resemble the following:
USERENV(ac.150) 10:00:04:554 PingComputer: First time: 0For more information about how to enable debug logging, click the following article number to view the article in the Microsoft Knowledge Base:
USERENV(ac.150) 10:00:04:554 PingComputer: Fast link. Exiting.
(http://support.microsoft.com/kb/221833/ )How to enable user environment debug logging in retail builds of Windows