First published on MSDN on Apr 08, 2008

Sporadic “Connection forcibly closed by remote host” errors with SQL Server connections can be very difficult to troubleshoot and resolve. This blog post is targeted at diagnosing TOE/Chimney issues that may lead to this client error message. Chimney is a feature introduced in the Windows Server 2003 Scalable Networking Pack, which was included in Windows Server 2003 SP2. Chimney increases network performance when using a network card which implements TOE, TCP/IP Offload Engine, which is a hardware implementation of the TCP/IP stack.

The following are the symptoms to look for:

·         The client connection is sporadically failing with the message: “TCP Provider: Connection forcibly closed by remote host.” The client connection may, in addition, sometimes fail with the message: “General network error”.

·         There are no corresponding network-related error messages in the SQL Server instance’s ERRORLOGs. Normally, the “Connection forcibly closed by remote host” message on the client indicates that an error occurred on the server which is deemed severe enough to close the connection; in that case, the server would log an error message explaining why the connection was closed. An example error message for this would be Error 17828: “The prelogin packet used to open the connection is structurally invalid; the connection has been closed. Please contact the vendor of the client library.” However, if the issue is in the networking hardware, such as a TOE-related issue, there will be no message in the SQL Server instance’s ERRORLOGs for this connection closure, since the server is not intentionally closing the connection. Therefore, check the SQL Server ERRORLOG for an absence of any corresponding network-related error messages.

·         There is no other client killing the first client’s connection. In addition to potential network hardware causes, the “Connection forcibly closed” message can also appear with no corresponding server ERRORLOG message if the client’s connection is being killed by a different client. Examine the SQL Server ERRORLOG for KILL statements; if there are none, then no other client is killing SQL Server connections.

If all three of these symptoms are appearing, your problem is likely due to a faulty piece of network hardware, possibly due to TOE/Chimney.

To test if TOE/Chimney is the source of your problem, you can disable it and see if the problem goes away. You should do this for BOTH the client and server, since TOE/Chimney on either machine, or both, could be the cause of the issue. To disable Chimney, run this command (if on Windows Vista or Windows Server 2008, run it at an elevated command prompt):

netsh int ip set chimney DISABLED

This command does NOT require a reboot. If you have these symptoms and running this command doesn’t fix the problem, then you likely have an issue with network hardware and should follow up by investigating your network hardware. This kb article should give you some leads on how to begin network troubleshooting: http://support.microsoft.com/kb/325487

Dan Benediktson
SQL Server Protocols
Disclaimer: This posting is provided "AS IS" with no warranties, and confers no rights