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Q232476: Terminal Server Connections and Logon Limited by MaxWorkItems

Article: Q232476
Product(s): Microsoft Windows NT
Version(s): 4.0,4.0 SP4
Operating System(s): 
Keyword(s): kbenv kbnetwork
Last Modified: 06-AUG-2002

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The information in this article applies to:

- Microsoft Windows NT Server versions 4.0, 4.0 SP4, Terminal Server Edition 
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IMPORTANT: This article contains information about modifying the registry. Before you 
modify the registry, make sure to back it up and make sure that you understand how to restore 
the registry if a problem occurs. For information about how to back up, restore, and edit the 
registry, click the following article number to view the article in the Microsoft Knowledge Base:

  Q256986 Description of the Microsoft Windows Registry

SYMPTOMS
========

After multiple Terminal Server clients establish a session with a server running
Microsoft Windows NT Server 4.0, Terminal Server Edition, additional clients are
unable to connect. When this occurs, in some cases, clients are not able to
browse certain servers or domain controllers after a specific number of client
sessions have been established. They may not exhibit the same symptoms as above,
but this issue may be corrected by the solution below.

This behavior is not affected by either the number of licenses in place or the
License Logging Service on either the Terminal Server computer or domain
controller. This problem can occur with either Independent Computing
Architecture or Remote Desktop Protocol clients, and the clients may receive one
of the following error messages:

  System could not log you on because domain <<domainname>> is not
  available

  -or-

  You do not have access to logon to this session

Clients are able to use the NET VIEW, NET USE, or the PING command to contact
other servers and domain resources without difficulty. In some cases, after 20
or 30 minutes, additional clients may be able to log on before new connections
are again refused. Central Processing Unit (CPU) usage is normally very low, and
this can occur regardless of the CPU speed, number of CPUs, or amount of Random
Access Memory (RAM) installed on either the Terminal Server computer or domain
controllers.

If the Terminal Server computer is a member server, no Event Viewer System log
entries may be evident. On the domain controllers, the Terminal Server
computer's Event Viewer System log may contain one or both of the following
entries:

  Error 1727: The remote procedure call failed and did not execute

  -or-

  Event ID: 1311
  Source: NetLogon
  Description: There are currently no logon servers available to service the
  logon request.

Other RPC error messages that may appear are:

  Error 1722: The RPC server is unavailable.

  Error 1723: The RPC server is too busy to complete this operation.

  Error 1721: Not enough resources are available to complete this operation.

  Netlogon Event ID 5719:
  No Windows NT Domain Controller is available for domain domain_name.
  The following error occurred:
  There are currently no logon servers available to service the logon request.


RESOLUTION
==========

To resolve this issue, you need to either edit the existing values or add the
following registry entries for both MaxWorkItems and MaxMpxCt to the server(s)
from which the clients are requesting resources. By default, MaxWorkItems and
MaxMpxCt do not appear under the parameters key although they are in effect.

MaxMpxCt allows a server to provide a "suggested" maximum number of simultaneous
client requests to itself, and then enforces those limits. Because each "client
connection" generates multiple instances (Windows shell, Explorer.exe, etc.),
with multiple clients connecting to the server, they can exceed the default
MaxMpxCt setting of 50. Once this limit is reached for that server, additional
requests are refused until it once again drops below the set limit.

NOTE: These values need to be added with such a ratio that the value for
MaxWorkItems is at least four times as large as that for MaxMpxCt. For example,
if MaxMpxCt has a value of 1024, then MaxWorkItems needs to have a value of at
least 4096.


WARNING: If you use Registry Editor incorrectly, you may cause serious problems
that may require you to reinstall your operating system. Microsoft cannot
guarantee that you can solve problems that result from using Registry Editor
incorrectly. Use Registry Editor at your own risk.

1. Start Registry Editor (Regedt32.exe).

2. Locate the following key in the registry:

  HKEY_LOCAL__MACHINE\System\CurrentControlSet\Services\LanmanServer\Parameters

3. Double-click the MaxWorkItems value, type "4096" (without the quotation
  marks), click Decimal, and then click OK.

  The number value you enter is arbitary, and you could also enter 8192, 16384,
  or 32768 if desired. However it is recommended to begin at the lower levels
  and work up as needed, doubling the value each time. The range for this value
  is 1 through 65535. If this value already exists, but you are experiencing
  problems similar to those outlined above, then edit this entry and double its
  current value but please choose a minimum value of 4096; For example, if it
  shows a value of 2048, then change it to 4096, and so forth. If problems
  persist, then continue this process until the issue subsides.

  NOTE: This value needs to be at least four times as large as MaxMpxCt.

4. If the MaxWorkItems value does not exist in the Parameters key, on the Edit
  menu, click Add Value, and then add the following registry value:

  

  Value Name: MaxWorkItems
  Data Type:  REG_DWORD
  Value:      4096

5. Double-click the MaxMpxCt value, type "1024" (without the quotation marks),
  click Decimal, and then click OK.

  The default value for MaxMpxCt is 50, but remember that MaxWorkItems needs to
  be set at least 4 times as high as the number used for MaxMpxCt.

  NOTE: Windows 95 and Windows 98 clients can interpret this registry entry
  differently than Windows NT, so apply this value according to which client is
  being used. For more information about how Windows 95 and Windows 98 does
  this, please click the article number below to view the article in the
  Microsoft Knowledge Base:

  Q232890 Win98 Fails to connect to NT4 share -- net client hangs.

6. If the MaxMpxCt value does not exist in the Parameters key, on the Edit menu,
  click Add Value, and then add the following registry value:

  

  Value Name: MaxMpxCt
  Data Type:  REG_DWORD
  Value:      1024 (Decimal)

  IMPORTANT: When you add this value to the registry of a computer running
  Windows 9x, set this value to 510 Decimal (or 1fe Hex).

NOTE: If Windows 95, Windows 98, and Windows NT clients are present, then the
value for MaxMpxCt should be set to the default used for Windows95 and Windows
98, because Windows NT should read the value without problems.



7. Quit Registry Editor and restart the computer.

MORE INFORMATION
================

Default MaxWorkItems Value:

This value specifies the maximum number of receive buffers, or work items, that
the Server service is permitted to allocate at one time. If this limit is
reached, then the transport must initiate flow control, which can significantly
impair performance. In some cases, this problem may also manifest itself by not
allowing new connections to be made to the server.

There is no set default value for this entry, because it is determined by the
computer's hardware configuration and the Server service, and may need to be
adjusted. Third-party programs may also require this value to be set at a higher
number.

Windows NT uses the settings for Server Service Optimization along with the
hardware configuration to help determine what the default value for MaxWorkItems
are. The Server Optimization choices are found in the Server properties when you
click the Services tab in Control Panel Network tool. Windows NT configures the
value in the following manner:

  (4*(MB*SMBServerPerfSetting)*OSVersion/1)*(#Processors)

where:

  MB = Megabytes RAM on the server
  SMBServerPerfSetting = .5 if "Minimize Memory Used"
  SMBServerPerfSetting = 1 if "Balance"
  SMBServerPerfSetting = 2 if "Maximize Throughput for File Sharing"
  OSVersion = 2 if running NTServer with > 16MB RAM
  #Processors = is the number of processors in the system

For example a server with one processor that is configured for Maximum Throughput
for File Sharing, the calculations for and 24 MB and 56 MB of RAM are
respectively:

  (4 * ( 24 * 2 ) * 2 / 1) * 1 = 384

  (4 * ( 56 * 2 ) * 2 / 1) * 1 = 896

Default MaxMpxCt values:

This allows a server to provide a suggested maximum number of simultaneous
outstanding client requests to a particular server. During negotiation of the
Server Message Block dialect, this value is passed to the client's redirector
where the limit on outstanding requests is enforced. A higher value can increase
server performance, but requires higher use of server work items (MaxWorkItems).
Because each client can consume multiple instances, this can exceed the default
maximum of 50.

For additional information about MaxMpxCt and slow network performance, please
click the article number below to view the article in the Microsoft Knowledge
Base:

  Q191370 Slow Network Performance with Terminal Server

This article does not apply to Windows 2000. In the following registry key, all
values greater than 125 are ignored:

  HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManServer\Parameters\MaxMpxCt

Additional query words: Lock Freeze hang logging

======================================================================
Keywords          : kbenv kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbNTTermServ400 kbNTTermServ400sp4 kbNTTermServSearch
Version           : :4.0,4.0 SP4
Issue type        : kbprb

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