Unable to Connect from TCP Ports Above 5000

• Microsoft Windows NT Server versions 3.51, 4.0
• Microsoft Windows NT Server, Enterprise Edition version 4.0
• Microsoft Windows NT Workstation versions 3.51, 4.0

SYMPTOMS

When you attempt to set up TCP connections from ports above 5000, the local computer responds with a WSAENOBUFS (10055) error, which means:

An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full.

RESOLUTION

The default maximum number of ephemeral TCP ports for Microsoft Windows NT is 5000. A new parameter has been added to Windows NT 3.51 Service Pack 5 and to Windows NT 4.0. To increase the maximum number of ephemeral ports you must set the following registry parameter:

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.

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).

1. Start Registry Editor (Regedt32.exe).



2. Locate the following key in the registry:
   
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters



3. On the Edit menu, click Add Value, and then add the following registry value:
   
   Value Name: MaxUserPort
   Data Type: REG_DWORD
   Value: 65534 <for example>
   
   Valid Range: 5000-65534 (decimal) Default: 0x1388 (5000 decimal)
   
   Description: This parameter controls the maximum port number used when an application requests any available user port from the system. Normally, ephemeral (that is, short-lived) ports are allocated between the values of 1024 and 5000 inclusive.



4. Quit Registry Editor.

Q149532 Windows NT Clients Run Out of Ports

MORE INFORMATION

For additional information, please see the following white paper available on the Microsoft anonymous ftp server:

File Name: TCPIPIMP2.doc
Location : ftp://ftp.microsoft.com/bussys/winnt/winnt-docs/papers/
Title : "Microsoft Windows NT 3.5/3.51/4.0: TCP/IP Implementation Details"

Keywords : kbnetwork
Version : WinNT:3.51,4.0
Platform : winnt
Issue type : kbprb