INF: SQL Logs 17832 with Multiple TCP\IP Connection Requests

ID: Q154628

The information in this article applies to:

Microsoft SQL Server versions 6.0, 6.5

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.

SUMMARY

If SQL Server is hit with multiple and simultaneous TCP/IP connection requests, such as the case with World Wide Web servers, the requests are quickly rejected by responding with a TCP/IP Reset Frame.

This symptom is difficult to detect. If the client application includes error code handling, the native error code is 10061 (WSAECONNREFUSED) for the Open() function. On the server, Error 17832 - "Unable to read login packet" appears in the SQL Error log.

If you trace this problem with a protocol analyzer, you can see that some of the connection request frames have been replied to with the TCP Reset bit set, which tells the sending station that the frame has been received, but the server does not have the resources to process the connection request.

MORE INFORMATION

A Winsock application accepts connections on a port by calling a Listen() function, which has a backlog parameter specifying the maximum length of the pending-connection queue. The Winsock specification defines the maximum Listen() backlog at five and when it exceeds five, TCP/IP issues a Reset.

The backlog for SQL Server can be configured to handle a great number of pending connections by modifying the Windows NT Registry. In some cases, the connection reset issue is resolved due to the modification.

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).

Start Registry Editor (REGEDT32.EXE) and locate the following Registry subkey in the HKEY_LOCAL_MACHINE subtree:


      \Software\Microsoft\MSSQLServer\MSSQLServer

NOTES:

The corresponding registry subkey in the HKEY_LOCAL_MACHINE subtree for SQL 4.21a is:
```
         \Software\Microsoft\SQLServer\Server
    
```

If SQL Server 6.5 Enterprise Edition is running with a Virtual SQL Server in a clustered environment, you must make the change to virtual server key, rather than the standard:
```
         \Software\Microsoft\MSSQLServer\MSSQLServer
    
```
This virtual server key is:


         \Software\Microsoft\MSSQLServer$VirtualServerName
         \MSSQLServer$VirtualServerName

         Value Name: WinsockListenBacklog
         Data Type:  REG_DWORD
         Data:       190

Select the MSSQLServer subkey. From the Edit menu, select Add Value.

Enter the following:
```
      Value Name: WinsockListenBacklog
      Data Type:  REG_DWORD
      Data:       <Range is 1 to 0xFFFFFFFF>
 
```
NOTE: The data value affects overall system resources if it is set to a high value. Windows NT 3.51 has a maximum overall backlog of 100 and Windows NT 4.0 has a maximum overall backlog of 200 for all applications. The suggested method of testing with this value is to set the value in increments of five and observe the results until the connection reset stops.

Click OK and quit Registry Editor.

Shut down and restart Windows NT.

For more information on the Listen() function, refer to the WIN32 SDK Programmer's reference.

For more information on the backlog parameter and Windows NT, please see the following two articles in the Microsoft Knowledge Base:

Q113576 : WinSocket App's Reject Connection Requests with Reset Frames

Q127144 : Windows NT 3.5 Winsock Listen (Backlog) Parameter Limit

Additional query words: Internet Information Server IIS windows sockets

Keywords : kbnetwork SSrvLAN
Version : winnt:6.0,6.5
Platform : winnt
Issue type :