Windows NT Clients Run Out of Ports (149532)

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 on how to do this, view the "Restoring the Registry" online Help topic in Regedit.exe or the "Restoring a Registry Key" online Help topic in Regedt32.exe.

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:

256986 Description of the Microsoft Windows Registry

CAUSE

This behavior can occur because computers that run Microsoft Windows NT clients and use excessive numbers of ports (more than 3,976 simultaneously) may run out of ports before TCP/IP releases closed connections. The TCP/IP-state computer 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. Since one MSL is defined as 120 seconds, it takes four minutes for a closed connection to be released in TCP/IP.

NOTE: For more information on MSL and Time-wait, please refer to Internet RFC 793.

WORKAROUND

To resolve this behavior, you must make the following registry change:

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.

HKEY_LOCAL_MACHINE\System\CurrectControlSet\services\Tcpip\Parameters

The registry value is:

TcpTimedWaitDelay

Key: Tcpip\Parameters
Value Type: REG_DWORD - Time in seconds
Valid Range: 30-300 (decimal)
Default: 0xF0 (240 decimal)

STATUS

Microsoft has confirmed this to be a problem in Microsoft Windows NT Workstation version 3.51 and Microsoft Windows NT Server version 3.51. This problem was corrected in the latest U.S. Service Pack for Windows NT Workstation or Server version 3.51. For information on obtaining this update, query "servpack" (without the quotation marks) in the Microsoft Knowledge Base.

MORE INFORMATION

For additional information about configuration options for Windows NT 4.0, click the article number below to view the article in the Microsoft Knowledge Base:

170359 How to Modify TCP/IP Maximum Retransmission Timeout