WINS Randomize1cList Feature Aids Load-Balancing Between DCs

ID: Q231305

The information in this article applies to:

Microsoft Windows NT Server, Enterprise Edition version 4.0

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SYMPTOMS

You are experiencing logon and network validation problems on a network in which workstations and their associated domain controllers (DCs) reside on different subnets. This network is also configured to use WINS as the main vehicle for name resolution.

If domain controllers are monitored, one is found to be much more heavily loaded than the others. Monitoring the overloaded DC, and network traffic to and from it, reveals the following:

In Server Manager, you may see the following:

A large number (hundreds) of connections to Pipe\Lsarpc.

In Network Monitor captures of network traffic, you may see the following:

Connections are frequently not made or transaction performed on Pipe\Lsarpc.

Typical Server Message Block error message codes include STATUS_IO_TIMEOUT and STATUS_PIPE_NOT_AVAILABLE.

In Performance Monitor, you may see the following:

A large Handle Count in the LSASS process.

A large Thread Count in the LSASS process (300 - 700+).

A combined high CPU usage (approaching 100 percent) by the LSASS and System processes.

NOTE: As the LSASS Thread Count increases, the proportion of CPU time used by the System process versus that used by LSASS increases because of increased context switching between the LSASS threads.

Detailed analysis of Network Monitor captures of network traffic generated when a workstation is restarted and logs on to the network reveals that the most overloaded DC is the DC whose IP address is the first in the list of IP addresses returned in WINS domainname<1C> name query responses.

A new WINS server feature, Randomize1cList, is now available and can promote more even load balancing between DCs in these specific circumstances. For example, where the overloaded DC is the DC whose IP address is the first in the domainname<1C> list).

CAUSE

In a network that uses WINS for name resolution, a workstation's logon server is selected as follows:

The workstation broadcasts a SAM logon request on its local subnet.

The workstation sends a WINS name query for domainname<1C> to its WINS server, which returns a list of up to 25 Domain Controller IP addresses, and the workstation sends a directed SAM logon request to each listed DC IP address in turn.

The order in which these directed SAM logon requests are issued is determined by the order of the IP addresses in the WINS domainname<1C> name query response; the first SAM logon request is sent to the first address in the list, and so on. The first DC to respond to a SAM logon request (broadcast or directed) is selected as the workstation's Logon Server.

If there are DCs on the workstation's subnet, one of these local DCs is usually selected as the workstation's logon server, as it receives the first broadcast SAM logon request earlier than remote DCs, and is therefore more likely to respond sooner than the remote DCs.

If there is no DC on the workstation's subnet, one of the DCs whose IP address appears in the domainname<1C> name query response is selected as the workstation's logon server. Normally, all the directed SAM logon requests are issued rapidly one after the other, and the first response is likely to be from the least busy DC. Over time, the usual result is each DC will become the logon server for a roughly equal numbers of workstations.

However, in some situations, it is possible for one of the remote DCs to be regularly selected as a workstation's logon server, causing it to become overloaded by subsequent volumes of validation traffic.

RESOLUTION

Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, please see the following article in the Microsoft Knowledge Base:

Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

Windows NT 3.51

A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp

The English version of this fix should have the following file attributes or later:


   Date      Time     Size      File name   Platform
   --------------------------------------------------
   06/08/98  06:23p   170,400   Wins.exe    x86
   06/08/98  06:24p   310,544   Wins.exe    Alpha

How to Activate Randomize1cList

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. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).
After you apply the hotfix, you can activate Randomize1cList by modifying the registry as described below.

WARNING: In most networks, there should be no need to activate this feature. In some situations, it could actually have an adverse effect, depending on where the DCs in the domainname<1C> list are located. For example, changing the order of the list might cause workstations in London to select logon servers in Hong Kong. It is recommended that you activate Randomize1cList ONLY after performing a thorough network analysis, and confirming that doing so is appropriate to the observed symptoms along with your WINS and network configurations.

To activate the Randomize1cList feature after installing the fix:

Start Registry Editor (Regedt32.exe).

From the HKEY_LOCAL_MACHINE subtree, go to the following key:

\SYSTEM\CurrentControlSet\Services\Wins\Parameters

From the Edit menu, click Add Value.

Add the following:


   Value Name: Randomize1cList
   Data Type:  REG_DWORD
   Data:       00000001
   Radix:      Hex

This key determines whether the WINS server changes the order of IP addresses in successive domainname<1C> name query responses. In certain situations, this change can improve load-balancing between domain controllers acting as logon servers within a domain.


Value: 0
Meaning: 1C List Randomization is not enabled. The WINS server returns the
list of IP addresses in WINS domainname&lt;1C&gt; name query responses in
the same order each time such a name query is made.

Value: 1   
Meaning: Enables 1C List Randomization. The WINS server rotates the list of
IP addresses in WINS domainname&lt;1C&gt; name query responses a random
amount each time such a query is made.

STATUS

Microsoft has confirmed this to be a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.

MORE INFORMATION

If there are no local DCs, one scenario that might lead to uneven laod balancing between DCs is network or router congestion. This can cause transmission delays between successive directed security account manager (SAM) logon requests. If such a transmission delay approaches the time required to receive a SAM logon request response from the first server in the DC IP address list, then it is likely that this DC will become the logon server for the bulk of the workstations in the domain.

An enhancement has been made to Wins.exe to provide a Randomize1CList feature to overcome this potential problem. With the Randomize1CList feature activated, the list of IP addresses in successive domainname<1C> name query responses is rotated a random amount before transmission to the workstation. This ensures a more even loading of DCs in problem scenarios, as described above.

Additional query words: wts tse RoundRobin Round Robin

Keywords :
Version : winnt:4.0
Platform : winnt
Issue type : kbbug