Terminal Server Client Connections and Logon Limited by MaxWorkItem and MaxMpxCt Values

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Article ID: 232476 - View products that this article applies to.
This article was previously published under Q232476
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This article applies to Windows 2000. Support for Windows 2000 ends on July 13, 2010. The Windows 2000 End-of-Support Solution Center is a starting point for planning your migration strategy from Windows 2000. For more information see the Microsoft Support Lifecycle Policy.
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SYMPTOMS

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

This behavior is not affected by either the number of licenses in position 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 can 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 can log on before new connections are refused again. CPU usage is typically 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 appear. 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 must either edit the existing values or add the following registry entries for both MaxWorkItems and MaxMpxCt to the servers 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 permits 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 (for example, Windows shell and Explorer.exe), with multiple clients connecting to the server, they can be greater than the default MaxMpxCt setting of 50. As soon as this limit is reached for that server, additional requests are refused until it drops below the set limit again.

Note: These values must 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.

Windows NT

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
  1. Start Registry Editor.
  2. Locate the following key in the registry:
    HKEY_LOCAL__MACHINE\System\CurrentControlSet\Services\LanmanServer\Parameters
  3. Double-click the MaxWorkItems value, type 4096, click Decimal, and then click OK.

    The number value you enter is arbitrary, and you can also enter 8192, 16384, or 32768 if you want to. However, Microsoft recommends that you start at the lower levels and work up as needed, doubling the value each time. The range for this value is one through 65535. If this value already exists, but you are experiencing problems similar to those outlined earlier, then edit this entry and double its current value but select a minimum value of 4096. For example, if it shows a value of 2048, then change it to 4096. If the problems persist, then continue this process until the issue subsides.

    Note: This value must be at least four times as large as the MaxMpxCt value.
  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, click Decimal, and then click OK.

    The default value for MaxMpxCt is 50, but remember that MaxWorkItems must be set at least four 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 additional information about how Windows 95 and Windows 98 interpret the registry entry differently than Windows NT, click the article number below to view the article in the Microsoft Knowledge Base:
    232890 Windows 98 Client Unable to Connect to Windows NT Share
  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 95, Windows 98, and Windows 98 Second Edition, set this value to 510 Decimal (or 1fe Hexadecimal). If Windows 95, Windows 98, and Windows NT clients are present, then the value for MaxMpxCt must be set to the default used for Windows95 and Windows 98, because Windows NT reads the value without problems.
  7. Quit Registry Editor and restart the computer.

Windows 2000

Note: You may experience a slow network response, and slow file copy performance when many people are using the Terminal server.

On a computer that is running Windows 2000 SP2 or later, follow these steps:
  1. Start Registry Editor.
  2. Locate, and then click the MaxCmds value under the following key in the registry:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation \Parameters
  3. On the Edit menu, click DWORD, type 500, and then click OK.
  4. Quit Registry Editor.
  5. On the remote server, start Registry Editor.
  6. Locate, and then click the following key in the registry:
    HKEY_LOCAL__MACHINE\System\CurrentControlSet\Services\LanmanServer\Parameters
  7. On the Edit menu, click Add Value, and then add the following registry values:
    Value name: MaxWorkItems
    Data type: REG_DWORD
    Radix: Decimal
    Value data: 8192

    -and-

    Value name: MaxMpxCt
    Data type: REG_DWORD
    Radix: Decimal
    Value data: 500
    Note: You may have to increase these values if the registry key does not work.
  8. Quit Registry Editor.
  9. Restart both servers.
For additional information about clients being unable to connect, click the article number below to view the article in the Microsoft Knowledge Base:
232890 Windows 98 Client Unable to Connect to Windows NT Share
For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:
271148 MaxMpxCt and MaxCmds Limits in Windows 2000

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 reduce performance. In some cases, this problem may also become evident by not permitting 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 have 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 and the hardware configuration to help determine what the default value for MaxWorkItems is. 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 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 permits 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 more use of server work items (MaxWorkItems). Because each client can consume multiple instances, this may be greater than the default maximum of 50.

317249 How to Troubleshoot Event ID 2021 and Event ID 2022

Properties

Article ID: 232476 - Last Review: November 1, 2006 - Revision: 3.5
APPLIES TO
  • Microsoft Windows 2000 Server
  • Microsoft Windows NT Server 4.0, Terminal Server Edition
Keywords: 
kbenv kbnetwork kbprb KB232476

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