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Microsoft KB Archive/170791

From BetaArchive Wiki

Windows 95 TCP Clients Run Out of Ports


The information in this article applies to:

  • Microsoft Windows 95
  • Microsoft Windows 95 OEM Service Release, versions 1, 2, 2.1

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.


When you are running programs in Windows 95 that use excessive numbers of TCP ports (more than 3976 simultaneously), Windows may run out of TCP ports before the TCP/IP protocol releases closed connections.


The TCP/IP state dictates that when a connection is closed, the connection is not released until two maximum segment lives (MSLs) have passed. This state is defined as the TIME-WAIT state. One MSL is defined as 120 seconds, and it takes four minutes for a closed connection to be released in TCP/IP.


This issue is resolved by the following updated file for Windows 95 and OSR2, and later versions of this file:

   VTCP.386  version 4.00.953  dated 4/21/97  47,413 bytes 

A version of this file that also resolves this problem is included in the Windows Sockets 2.0 Update for Windows 95. For information about obtaining this update, see the following article in the Microsoft Knowledge Base:

Q182108 Availability of Windows Sockets 2.0 for Windows 95


Microsoft has confirmed this to be a problem in Microsoft Windows 95 and OEM Service Release 2 (OSR2). An update to address this problem is now available, but is not fully regression tested and should be applied only to computers experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft does not recommend implementing this update at this time. Contact Microsoft Technical Support for additional information about the availability of this update.

This issue is resolved in Microsoft Windows 98.


This update adds a new registry entry to TCP/IP to allow the TIME-WAIT state to be configurable. This allows TCP/IP users to free closed connection resources more quickly. This entry also allows setting the Maximum Retransmission Timeout for a TCP connection.

By default, when the retransmission timer hits 240 seconds (MSL * 2), it uses that value for the retransmission of any segment that needs to be retransmitted. This can be a cause of long delays on a slow link.

You can adjust this timeout value with the entry listed below.

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.

After installing the update, add the following registry value and set it to the appropriate value:

      Value Type: String
      Valid Range: 30-300 (decimal)
      Default: 240 

For additional information about issues resolved by updates to this component, please see the following articles in the Microsoft Knowledge Base:

Q178022 NetBIOS SEND WAIT Over TCP/IP Completes Without NetBIOS RECEIVE

Q177539 Windows 95 Stops Responding Because of Land Attack

Q168747 Update to Windows 95 TCP/IP to Address Out-of-Band Issue

Q154579 Slow TCP/IP Performance When Resuming Large Data Transfer

For additional information about Windows 95 updates, please see the following article in the Microsoft Knowledge Base:

Q161020 Implementing Windows 95 Updates

Additional query words:

Keywords : kbnetwork osr1 osr2 win95
Issue type :
Technology : kbWin95search kbOPKSearch kbWin95 kbWin95OPKOSR2 kbWin95OPKOSR1 kbWin95OPKOSR210

Last Reviewed: January 31, 2001
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