Type of Service Octet in IP Header Not Initialized

The Type of Service (TOS) octet is not initialized to zero for Windows NT 4.0 Service Pack 4 and later builds on the Alpha and x86 platforms. This results in a random value for the Precedence field in the TOS octet. Some third-party vendor's TCP/IP stacks may require that the Precedence field be set to zero, and they will send a reset to any host that does not meet this requirement, thus causing sessions between Windows NT and such hosts to fail unless the Precedence field happens to get randomly initialized to zero on Windows NT.

To work around this problem, statically start the TOS octet by setting the DefaultTOS value in the registry to some non-zero value. For additional information about how to modify the DefaultTOS value, please see the following article(s) in the Microsoft Knowledge Base:
To resolve this problem, obtain the latest service pack for Windows NT 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this is a problem in Window NT 4.0. This problem was first corrected in Windows NT version 4.0 Service Pack 5.

IBM mainframe hosts are IP hosts that are known to have this problem. The IP stack configuration on IBM mainframes can be configured to accept nonzero values in the Precedence field. Please see your IBM operating system documentation for information on how to make the necessary changes.

The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.

Additional information is available in the following RFCs:

• RFC 791, Internet Protocol -- DARPA Internet Program Protocol Specification
• RFC 1349, Type of Service in the Internet Protocol Suite