NWLink SPX Ignores Allocation Number Sent By Peer

• Microsoft Windows NT Workstation version 4.0 Service Pack 3
• Microsoft Windows NT Server version 4.0 Service Pack 3

SYMPTOMS

Under certain conditions, computers that connect to a process on a Windows NT computer may fail. For example, the computer may time-out, applications may stop responding, or the computer may disconnect. On the network you may also see increased retransmissions.

This has been observed with SQL server where clients access the database using ODBC over SPX but it may happen with any SPX-based communication.

CAUSE

The SQL server numbers the frames (for example, 23) when it sends data to the client. The client indicates that it has received the frame and specifies with an Allocation Number if it can receive another frame (for example, 24).

If the client-side SPX protocol cannot receive another frame because the process did not copy the data and gave it another buffer, it does not increment its Allocation Number (for example, send 23). This is especially true for database applications as they may perform a considerable amount of work locally.

The sending station should refrain from sending frames until it receives another frame with an updated Allocation Number. The problem introduced in Service Pack 2 is that Windows NT NWLink SPX ignores the Allocation Number field and continues to send frames. After this happens, one of the stations eventually decides that the session is out of synch and disconnects.

When the connection starts over the two stations are likely to run into the same problem again.

RESOLUTION

To work around this problem, use a different communication protocol. Depending on the existing installation this might not be possible.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.