Limit of 49 Named Pipe Connections from a Single Workstation

• Microsoft Windows NT Workstation versions 3.5 and 3.51
• Microsoft Windows NT Server versions 3.5 and 3.51

SYMPTOMS

A named pipe server application running on a Windows NT Server creates a large number (for example, 100) of separate, distinct named pipes (for example, \\pipe\pipe001, \\pipe\pipe002, etc.).

A named pipe client application then tries to connect to all of the named pipes created by the server application.

If the named pipe client is running on the same computer as the named pipe server, the client can successfully simultaneously connect to all the named pipes created by the server application. However, if the named pipe client is running on a Windows NT Workstation, the client can connect to only 49 of the server's named pipes across the network.

CAUSE

This limit on the number of network connections to named pipes from a single client is imposed by the MaxMpxCt registry value for the LanmanServer service on the Windows NT Server.

MORE INFORMATION

The MaxMpxCt Registry value is described as follows in the Windows NT Resource Kit Registry Help file:

Registry path:

HKEY_LOCAL_MACHINE\SYSTEM

   \CurrentControlSet
      \Services
         \LanmanServer
            \Parameters

MaxMpxCt     REG_DWORD

Provides a suggested maximum to clients for the number of simultaneous requests outstanding to this server. A higher value can increase server performance but requires higher use of server work items.

RESOLUTION

Either increase the server's MaxMpxCt registry value, or redesign the client/server application to use fewer named pipes. Redesigning the client/server application is recommended, because this minimizes server resource usage and results in a much more scaleable solution.